fix($browser): should use first value for a cookie.

With this change, $browser.cookies()["foo"] will behave like
docCookies.getItem("foo") where docCookies is defined at
https://developer.mozilla.org/en-US/docs/DOM/document.cookie

Ref: https://github.com/angular/angular.js/issues/2635

This fixes the issue where, if there's a value for the XSRF-TOKEN cookie
value with the path /, then that value is used for all applications in
the domain even if they set path specific values for XSRF-TOKEN.