Enforce ES2015 syntax

The whole project is going to use ES2015, so it's important to
enforce usage of the new syntax to the project code homogeneous.
This commit enforces usage of arrow functions where possible,
let/const instead of var and rest/spread operator instead of
arguments and call/apply.

Change-Id: I2fd33400d7d4a3ed23363ceaaf0c2d2f1bd55c47

.eslintrc

@@ -3,3 +3,24 @@ extends: openstack
 parserOptions:
   ecmaVersion: 6
   sourceType: module
+
+rules:
+  # disallow unnecessary .call() and .apply()
+  # http://eslint.org/docs/rules/no-useless-call
+  no-useless-call: 2
+
+  # require let or const instead of var
+  # http://eslint.org/docs/rules/no-var
+  no-var: 2
+
+  # suggest using arrow functions as callbacks
+  # http://eslint.org/docs/rules/prefer-arrow-callback
+  prefer-arrow-callback: 2
+
+  # suggest using the spread operator instead of .apply().
+  # http://eslint.org/docs/rules/prefer-spread
+  prefer-spread: 2
+
+  # suggest using the rest parameters instead of arguments
+  # http://eslint.org/docs/rules/prefer-rest-params
+  prefer-rest-params: 2

test/unit/indexTest.js

@@ -2,7 +2,7 @@ import Test from "../../src/index.js";
 
 describe("Simple test", () => {
   it("should export a class", () => {
-    var t = new Test();
+    let t = new Test();
     expect(t).toBeDefined();
   });
 });