Replace custom ESLint rule with builtin (#1546)

Author: IvanGoncharov

.eslintrc.yml

@@ -360,4 +360,10 @@ overrides:
   - files: "*"
     excludedFiles: "**/__tests__/**"
     rules:
-      no-async: error
+      no-restricted-syntax:
+        - error
+        - selector: 'FunctionDeclaration[async=true]'
+          message: >
+            async functions are not allowed outside of the test suite because
+            older versions of NodeJS do not support them without additional
+            runtime dependencies. Instead, use explicit Promises.

package.json

@@ -29,7 +29,7 @@
     "testonly": "mocha --require @babel/register --require @babel/polyfill --check-leaks --full-trace --timeout 15000 src/**/__tests__/**/*-test.js",
     "testonly:cover": "nyc --reporter html --reporter text-summary -- npm run testonly",
     "testonly:coveralls": "nyc --silent -- npm run testonly && nyc report --reporter text-lcov | coveralls",
-    "lint": "eslint --report-unused-disable-directives --rulesdir ./resources/lint src || (printf '\\033[33mTry: \\033[7m npm run lint -- --fix \\033[0m\\n' && exit 1)",
+    "lint": "eslint --report-unused-disable-directives src || (printf '\\033[33mTry: \\033[7m npm run lint -- --fix \\033[0m\\n' && exit 1)",
     "benchmark": "node ./resources/benchmark.js",
     "prettier": "prettier --write 'src/**/*.js'",
     "check": "flow check",

resources/lint/no-async.js

@@ -145,7 +145,7 @@ function lintFiles(filepaths) {
   return filepaths.reduce((prev, filepath) => prev.then(prevSuccess => {
     if (isJS(filepath)) {
       process.stdout.write('  ' + filepath + ' ...');
-      return exec('eslint', ['--rulesdir', './resources/lint', srcPath(filepath)])
+      return exec('eslint', [srcPath(filepath)])
         .catch(() => false)
         .then(success => {
           console.log(CLEARLINE + '  ' + (success ? CHECK : X)