avoid deprecated --compilers mocha flag

https://github.com/mochajs/mocha/wiki/compilers-deprecation

Author: graingert

package.json

@@ -16,8 +16,8 @@
  "publish-to-npm": "npm run build:readme && npm run dist && npm publish",
  "preversion": "npm run build:playground && npm run dist && npm run build:readme && npm run cs-check && npm run lint",
  "start": "node devServer.js",
- "tdd": "cross-env NODE_ENV=test mocha --compilers js:babel-register --watch --require ./test/setup-jsdom.js test/**/*_test.js",
- "test": "cross-env NODE_ENV=test mocha --compilers js:babel-register --require ./test/setup-jsdom.js test/**/*_test.js"
+ "tdd": "cross-env NODE_ENV=test mocha --require babel-register --watch --require ./test/setup-jsdom.js test/**/*_test.js",
+ "test": "cross-env NODE_ENV=test mocha --require babel-register --require ./test/setup-jsdom.js test/**/*_test.js"
  },
  "prettierOptions": "--jsx-bracket-same-line --trailing-comma es5 --semi --tab-width 2",
  "lint-staged": {