Update Holder.js to v2.6.0.

[ci skip]

docs/examples/carousel/index.html

@@ -209,7 +209,7 @@
     <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
     <script src="../../dist/js/bootstrap.min.js"></script>
     <!-- Just to make our placeholder images work. Don't actually copy the next line! -->
-    <script src="../../assets/js/vendor/holder.js"></script>
+    <script src="../../assets/js/vendor/holder.min.js"></script>
     <!-- IE10 viewport hack for Surface/desktop Windows 8 bug -->
     <script src="../../assets/js/ie10-viewport-bug-workaround.js"></script>
   </body>

docs/examples/dashboard/index.html

@@ -241,7 +241,7 @@
     <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
     <script src="../../dist/js/bootstrap.min.js"></script>
     <!-- Just to make our placeholder images work. Don't actually copy the next line! -->
-    <script src="../../assets/js/vendor/holder.js"></script>
+    <script src="../../assets/js/vendor/holder.min.js"></script>
     <!-- IE10 viewport hack for Surface/desktop Windows 8 bug -->
     <script src="../../assets/js/ie10-viewport-bug-workaround.js"></script>
   </body>

grunt/configBridge.json

@@ -11,7 +11,7 @@
       "../assets/js/src/customizer.js"
     ],
     "docsJs": [
-      "../assets/js/vendor/holder.js",
+      "../assets/js/vendor/holder.min.js",
       "../assets/js/vendor/ZeroClipboard.min.js",
       "../assets/js/vendor/anchor.js",
       "../assets/js/src/application.js"