no-global-assign should include all browser global variables when environment is browser

We're using Airbnb style guide. Today I faced a bug that root of it was the fact that I had a variable named `location` which is a global object available in browser. So instead of getting `variable not defined: location` ESLint just passed.

[no-global-assign](http://eslint.org/docs/rules/no-global-assign) accepts an array of variable names that should be forbidden to use. All variable names like `location`, `document`, `window` and `navigator` should be in the blacklist as variable names.

Start with the no-global-assign rule configuration described in the issue and inspect how this repository defines its ESLint rules. Check how browser globals such as location, document, window, and navigator are represented, then verify that the rule reports assignments to them when the environment is browser.

Written by the indexing model from the issue text.