Use strict mode in jQuery version check module. Closes #15535

Created by: peterblazejewicz

This PR adds strict mode declaration missing in jQuery version check module which is inserted at runtime via Grunt tasks to distribution source code. Missing use strict missed JSHint code checks as it is part of content not covered by JSHint tests.

After build the non-minified distribution file will look like:

diff --git a/dist/js/bootstrap.js b/dist/js/bootstrap.js
index 42e92bf..ab0ae1e 100644
--- a/dist/js/bootstrap.js
+++ b/dist/js/bootstrap.js
@@ -9,6 +9,7 @@ if (typeof jQuery === 'undefined') {
 }

 +function ($) {
+  'use strict';
   var version = $.fn.jquery.split(' ')[0].split('.')
   if ((version[0] < 2 && version[1] < 9) || (version[0] == 1 && version[1] == 9 && version[2] < 1)) {
     throw new Error('Bootstrap\'s JavaScript requires jQuery version 1.9.1 or higher')

and version check module will look like:

+function ($) {
  'use strict';
  var version = $.fn.jquery.split(' ')[0].split('.')
  if ((version[0] < 2 && version[1] < 9) || (version[0] == 1 && version[1] == 9 && version[2] < 1)) {
    throw new Error('Bootstrap\'s JavaScript requires jQuery version 1.9.1 or higher')
  }
}(jQuery);

Thanks!