Use one declaration per statement

The old style of merging all of a function's variable declarations into
a single statement made some sense back in the days of var, but there's
no reason to keep doing it now that we use const and let.

spec/core/UserContextSpec.js

@@ -1,7 +1,7 @@
 describe('UserContext', function() {
   it('Behaves just like an plain object', function() {
-    const context = new privateUnderTest.UserContext(),
-      properties = [];
+    const context = new privateUnderTest.UserContext();
+    const properties = [];
 
     for (const prop in context) {
       if (obj.hasOwnProperty(prop)) {