fix(directive): trim off white space around element.text()

Using the directive on an element containing white space results in 'Translation for ... doesn't exist'.
Changing the behaviour of the directive to trim off white space fixes this issue.
As trim() is unsupported on IE 8, replace() is chosen.

ngTranslate/directive/translate.js

@@ -22,10 +22,10 @@ angular.module('ngTranslate')
 
       // Ensures any change of the attribute "translate" containing the id will
       // be re-stored to the scope's "translationId".
-      // If the attribute has no content, the element's text value will be used.
+      // If the attribute has no content, the element's text value (white spaces trimmed off) will be used.
       attr.$observe('translate', function (translationId) {
         if (angular.equals(translationId , '')) {
-          scope.translationId = $interpolate(element.text())(scope.$parent);
+          scope.translationId = $interpolate(element.text().replace(/^\s+|\s+$/g,''))(scope.$parent);
         } else {
           scope.translationId = translationId;
         }

test/unit/translateDirectiveSpec.js

@@ -95,6 +95,14 @@ describe('ngTranslate', function () {
           expect(element.text()).toBe('foo');
         });
       });
+
+      it('should return translation if translation id exists and if its passed surrounded by white space', function () {
+        inject(function ($rootScope, $compile) {
+          element = $compile('<div translate>  TRANSLATION_ID  </div>')($rootScope);
+          $rootScope.$digest();
+          expect(element.text()).toBe('foo');
+        });
+      });
     });
 
     describe('Passing values', function () {