adjust filename to indicate that customize JS is minified

Gruntfile.js

@@ -127,7 +127,7 @@ module.exports = function (grunt) {
           'docs/assets/js/filesaver.js',
           'docs/assets/js/customizer.js'
         ],
-        dest: 'docs/assets/js/customize.js'
+        dest: 'docs/assets/js/customize.min.js'
       }
     },
 

docs/_includes/footer.html

@@ -9,7 +9,7 @@
 
 {% if page.slug == "customize" %}
 <script src="{{ site.baseurl }}assets/js/raw-files.js"></script>
-<script src="{{ site.baseurl }}assets/js/customize.js"></script>
+<script src="{{ site.baseurl }}assets/js/customize.min.js"></script>
 {% endif %}
 
 {% comment %}