merge mocharc.coverage into mocharc (#5385)

Author: milahu

.mocharc.coverage.js

@@ -3,3 +3,13 @@ module.exports = {
 		'test/test.js'
 	]
 };
+
+// add coverage options when running 'npx c8 mocha'
+if (process.env.NODE_V8_COVERAGE) {
+	Object.assign(module.exports, {
+		fullTrace: true,
+		require: [
+			'source-map-support/register'
+		]
+	});
+}

.mocharc.js

@@ -23,10 +23,10 @@
   },
   "types": "types/runtime/index.d.ts",
   "scripts": {
-    "test": "mocha --config .mocharc.js",
+    "test": "mocha",
     "test:unit": "mocha --require sucrase/register --recursive src/**/__test__.ts",
-    "quicktest": "mocha --config .mocharc.js",
-    "precoverage": "c8 mocha --config .mocharc.coverage.js",
+    "quicktest": "mocha",
+    "precoverage": "c8 mocha",
     "coverage": "c8 report --reporter=text-lcov > coverage.lcov && c8 report --reporter=html",
     "codecov": "codecov",
     "precodecov": "npm run coverage",