refactor: use document.documentMode to determine msie version

Closes angular#9398

Author: IgorMinar

src/Angular.js

@@ -173,13 +173,10 @@ var /** holds major version number for IE or NaN for real browsers */
     uid               = 0;
 
 /**
- * IE 11 changed the format of the UserAgent string.
- * See http://msdn.microsoft.com/en-us/library/ms537503.aspx
+ * documentMode is an IE-only property
+ * http://msdn.microsoft.com/en-us/library/ie/cc196988(v=vs.85).aspx
  */
-msie = int((/msie (\d+)/.exec(lowercase(navigator.userAgent)) || [])[1]);
-if (isNaN(msie)) {
-  msie = int((/trident\/.*; rv:(\d+)/.exec(lowercase(navigator.userAgent)) || [])[1]);
-}
+msie = document.documentMode;
 
 
 /**

src/ngScenario/browserTrigger.js

@@ -1,7 +1,11 @@
 'use strict';
 
 (function() {
-  var msie = parseInt((/msie (\d+)/.exec(navigator.userAgent.toLowerCase()) || [])[1], 10);
+  /**
+   * documentMode is an IE-only property
+   * http://msdn.microsoft.com/en-us/library/ie/cc196988(v=vs.85).aspx
+   */
+  msie = document.documentMode;
 
   /**
    * Triggers a browser event. Attempts to choose the right event if one is