chore: downgrade autoprefixer to v8.6.5

autoprefixer > v9 depends on a version of postcss that has a
vulnerability. Unfortunately, version autoprefixer > 10 does not work
with grunt-postcss. So to fix the vulnerability, autoprefixer has been
downgraded. This also is more consistent with other projects.

package-lock.json

@@ -1174,24 +1174,101 @@
       "dev": true
     },
     "autoprefixer": {
-      "version": "9.5.1",
-      "resolved": "https://registry.npmjs.org/autoprefixer/-/autoprefixer-9.5.1.tgz",
-      "integrity": "sha512-KJSzkStUl3wP0D5sdMlP82Q52JLy5+atf2MHAre48+ckWkXgixmfHyWmA77wFDy6jTHU6mIgXv6hAQ2mf1PjJQ==",
+      "version": "8.6.5",
+      "resolved": "https://registry.npmjs.org/autoprefixer/-/autoprefixer-8.6.5.tgz",
+      "integrity": "sha512-PLWJN3Xo/rycNkx+mp8iBDMTm3FeWe4VmYaZDSqL5QQB9sLsQkG5k8n+LNDFnhh9kdq2K+egL/icpctOmDHwig==",
       "dev": true,
       "requires": {
-        "browserslist": "^4.5.4",
-        "caniuse-lite": "^1.0.30000957",
+        "browserslist": "^3.2.8",
+        "caniuse-lite": "^1.0.30000864",
         "normalize-range": "^0.1.2",
         "num2fraction": "^1.2.2",
-        "postcss": "^7.0.14",
-        "postcss-value-parser": "^3.3.1"
+        "postcss": "^6.0.23",
+        "postcss-value-parser": "^3.2.3"
       },
       "dependencies": {
+        "ansi-styles": {
+          "version": "3.2.1",
+          "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-3.2.1.tgz",
+          "integrity": "sha512-VT0ZI6kZRdTh8YyJw3SMbYm/u+NqfsAxEpWO0Pf9sq8/e94WxxOpPKx9FR1FlyCtOVDNOQ+8ntlqFxiRc+r5qA==",
+          "dev": true,
+          "requires": {
+            "color-convert": "^1.9.0"
+          }
+        },
+        "browserslist": {
+          "version": "3.2.8",
+          "resolved": "https://registry.npmjs.org/browserslist/-/browserslist-3.2.8.tgz",
+          "integrity": "sha512-WHVocJYavUwVgVViC0ORikPHQquXwVh939TaelZ4WDqpWgTX/FsGhl/+P4qBUAGcRvtOgDgC+xftNWWp2RUTAQ==",
+          "dev": true,
+          "requires": {
+            "caniuse-lite": "^1.0.30000844",
+            "electron-to-chromium": "^1.3.47"
+          }
+        },
+        "chalk": {
+          "version": "2.4.2",
+          "resolved": "https://registry.npmjs.org/chalk/-/chalk-2.4.2.tgz",
+          "integrity": "sha512-Mti+f9lpJNcwF4tWV8/OrTTtF1gZi+f8FqlyAdouralcFWFQWF2+NgCHShjkCb+IFBLq9buZwE1xckQU4peSuQ==",
+          "dev": true,
+          "requires": {
+            "ansi-styles": "^3.2.1",
+            "escape-string-regexp": "^1.0.5",
+            "supports-color": "^5.3.0"
+          }
+        },
+        "color-convert": {
+          "version": "1.9.3",
+          "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-1.9.3.tgz",
+          "integrity": "sha512-QfAUtd+vFdAtFQcC8CCyYt1fYWxSqAiK2cSD6zDB8N3cpsEBAvRxp9zOGg6G/SHHJYAT88/az/IuDGALsNVbGg==",
+          "dev": true,
+          "requires": {
+            "color-name": "1.1.3"
+          }
+        },
+        "color-name": {
+          "version": "1.1.3",
+          "resolved": "https://registry.npmjs.org/color-name/-/color-name-1.1.3.tgz",
+          "integrity": "sha1-p9BVi9icQveV3UIyj3QIMcpTvCU=",
+          "dev": true
+        },
+        "has-flag": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-3.0.0.tgz",
+          "integrity": "sha1-tdRU3CGZriJWmfNGfloH87lVuv0=",
+          "dev": true
+        },
+        "postcss": {
+          "version": "6.0.23",
+          "resolved": "https://registry.npmjs.org/postcss/-/postcss-6.0.23.tgz",
+          "integrity": "sha512-soOk1h6J3VMTZtVeVpv15/Hpdl2cBLX3CAw4TAbkpTJiNPk9YP/zWcD1ND+xEtvyuuvKzbxliTOIyvkSeSJ6ag==",
+          "dev": true,
+          "requires": {
+            "chalk": "^2.4.1",
+            "source-map": "^0.6.1",
+            "supports-color": "^5.4.0"
+          }
+        },
         "postcss-value-parser": {
           "version": "3.3.1",
           "resolved": "https://registry.npmjs.org/postcss-value-parser/-/postcss-value-parser-3.3.1.tgz",
           "integrity": "sha512-pISE66AbVkp4fDQ7VHBwRNXzAAKJjw4Vw7nWI/+Q3vuly7SNfgYXvm6i5IgFylHGK5sP/xHAbB7N49OS4gWNyQ==",
           "dev": true
+        },
+        "source-map": {
+          "version": "0.6.1",
+          "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
+          "integrity": "sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==",
+          "dev": true
+        },
+        "supports-color": {
+          "version": "5.5.0",
+          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-5.5.0.tgz",
+          "integrity": "sha512-QjVjwdXIt408MIiAqCX4oUKsgU2EqAGzs2Ppkm4aQYbjm+ZEWEcW4SfFNTr4uMNZma0ey4f5lgLrkB0aX0QMow==",
+          "dev": true,
+          "requires": {
+            "has-flag": "^3.0.0"
+          }
         }
       }
     },

package.json

@@ -28,7 +28,7 @@
   "devDependencies": {
     "@silvermine/eslint-config": "3.0.1",
     "@silvermine/standardization": "1.1.0",
-    "autoprefixer": "9.5.1",
+    "autoprefixer": "8.6.5",
     "check-node-version": "4.0.3",
     "coveralls": "3.0.3",
     "eslint": "6.8.0",