Update for mocha@8

Author: anseki

Diff for: .mocharc.js

@@ -0,0 +1,9 @@
+'use strict';
+
+module.exports = {
+  spec: [
+    './test/functions.test.js',
+    './test/getCode.test.js',
+    './test/mangle.test.js'
+  ]
+};