Change math syntax (#3280)

src/mfm/parse/elements/math.ts

@@ -9,7 +9,7 @@ export type TextElementMath = {
 };
 
 export default function(text: string) {
-	const match = text.match(/^\$(.+?)\$/);
+	const match = text.match(/^\\\((.+?)\\\)/);
 	if (!match) return null;
 	const math = match[0];
 	return {

test/mfm.ts

@@ -266,7 +266,7 @@ describe('Text', () => {
 
 		it('math', () => {
 			const fomula = 'x = {-b \\pm \\sqrt{b^2-4ac} \\over 2a}.';
-			const text = `$${fomula}$`;
+			const text = `\\(${fomula}\\)`;
 			const tokens = analyze(text);
 			assert.deepEqual([
 				{ type: 'math', content: text, formula: fomula }