Fixes a typo 'use_strict' -> 'use strict'

Apparently strict mode is not enabled in toast widgets, due to a
'use_strict' typo, that must have crept in during jscs cleanup
This commit fixes the typo.

Closes-Bug: #1466003
Change-Id: I4cf30b8343bba6bbe7932e3927c6cbc8a81dc0df

horizon/static/framework/widgets/toast/toast.directive.js

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 (function() {
-  'use_strict';
+  'use strict';
 
   /**
     * @ngdoc directive

horizon/static/framework/widgets/toast/toast.factory.js

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 (function() {
-  'use_strict';
+  'use strict';
 
   /**
     * @ngdoc service
@@ -88,6 +88,7 @@
     function add(type, msg) {
       var toast = {
         type: type === 'error' ? 'danger' : type,
+        /* jshint validthis:true */
         typeMsg: this.types[type],
         msg: msg,
         cancel: cancel

horizon/static/framework/widgets/toast/toast.module.js

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 (function() {
-  'use_strict';
+  'use strict';
 
   /**
    * @ngdoc overview