Preserve parens with keyof, enforce parens with arrows with type params (#2503)

* Force parens around argument of simple arrow function if type annotation is present

* Preserve parens inside keyof operator

jest.config.js

@@ -8,7 +8,7 @@ module.exports = {
   testRegex: "jsfmt\\.spec\\.js$|__tests__/.*\\.js$",
   testPathIgnorePatterns: ["tests/new_react", "tests/more_react"],
   collectCoverage: ENABLE_COVERAGE,
-  collectCoverageFrom: ["src/**/*.js", "index.js"],
+  collectCoverageFrom: ["src/**/*.js", "index.js", "!<rootDir>/node_modules/"],
   coveragePathIgnorePatterns: [
     "<rootDir>/src/doc-debug.js",
     "<rootDir>/src/clean-ast.js",