Code style: Switched to ESLint. See #366.

.eslintrc.js

@@ -0,0 +1,12 @@
+/**
+ * @license Copyright (c) 2003-2017, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md.
+ */
+
+/* eslint-env node */
+
+'use strict';
+
+module.exports = {
+	extends: 'ckeditor5'
+};

gulpfile.js

@@ -3,17 +3,19 @@
  * For licensing, see LICENSE.md.
  */
 
+/* eslint-env node */
+
 'use strict';
 
 const path = require( 'path' );
 const gulp = require( 'gulp' );
 
 // Lint tasks. ---------------------------------------------------------------
 
-const ckeditor5Lint = require( '@ckeditor/ckeditor5-dev-lint' )();
+const ckeditor5Lint = require( '@ckeditor/ckeditor5-dev-lint' );
 
-gulp.task( 'lint', ckeditor5Lint.lint );
-gulp.task( 'lint-staged', ckeditor5Lint.lintStaged );
+gulp.task( 'lint', () => ckeditor5Lint.lint() );
+gulp.task( 'lint-staged', () => ckeditor5Lint.lintStaged() );
 gulp.task( 'pre-commit', [ 'lint-staged' ] );
 
 // Tests. ---------------------------------------------------------------------
@@ -42,7 +44,8 @@ gulp.task( 'docs', () => {
 	const umberto = require( 'umberto' );
 	const ckeditor5Docs = require( '@ckeditor/ckeditor5-dev-docs' );
 
-	return ckeditor5Docs.build( {
+	return ckeditor5Docs
+		.build( {
 			readmePath: path.join( process.cwd(), 'README.md' ),
 			sourceFiles: [
 				process.cwd() + '/packages/ckeditor5-*/src/**/*.@(js|jsdoc)',
@@ -106,8 +109,8 @@ function assertIsInstalled( packageName ) {
 		require( packageName + '/package.json' );
 	} catch ( err ) {
 		console.error( `Error: Cannot find package '${ packageName }'.\n` );
-		console.error( `You need to install optional dependencies.` );
-		console.error( `Run: 'npm run install-optional-dependencies'.` );
+		console.error( 'You need to install optional dependencies.' );
+		console.error( 'Run: \'npm run install-optional-dependencies\'.' );
 
 		process.exit( 1 );
 	}

package.json

@@ -35,8 +35,9 @@
     "@ckeditor/ckeditor5-widget": "^0.1.1"
   },
   "devDependencies": {
-    "@ckeditor/ckeditor5-dev-lint": "^2.0.2",
+    "@ckeditor/ckeditor5-dev-lint": "^3.0.0",
     "@ckeditor/ckeditor5-dev-tests": "^7.3.0",
+    "eslint-config-ckeditor5": "^1.0.0",
     "gulp": "^3.9.0",
     "guppy-pre-commit": "^0.4.0",
     "lerna": "^2.0.0-rc.1",