Add spec for GitHub issue 47

https://github.com/icy-arctic-fox/spectator/issues/47

spec/issues/github_issue_47_spec.cr

@@ -0,0 +1,18 @@
+require "../spec_helper"
+
+Spectator.describe "GitHub Issue #47" do
+  class Original
+    def foo(arg1, arg2)
+      # ...
+    end
+  end
+
+  mock Original
+
+  let(fake) { mock(Original) }
+
+  specify do
+    expect(fake).to receive(:foo).with("arg1", arg2: "arg2")
+    fake.foo("arg1", "arg2")
+  end
+end