tools: enable all es6 rules in linter

This change enables the es6 environment in eslint. Rather than selecting
es6 rules one at a time, this turns all of them on with the exception of
modules.

Ref: nodejs#5028

Author: Trott

.eslintrc

@@ -1,18 +1,6 @@
 env:
   node: true
-
-# enable ECMAScript features
-ecmaFeatures:
-  arrowFunctions: true
-  binaryLiterals: true
-  blockBindings: true
-  classes: true
-  forOf: true
-  generators: true
-  objectLiteralShorthandMethods: true
-  objectLiteralShorthandProperties: true
-  octalLiterals: true
-  templateStrings: true
+  es6: true
 
 rules:
   # Possible Errors