Fix trailing comma problem in generated bower.json.

Author: Kahlil Lechelt

app/templates/_bower.json

@@ -7,12 +7,8 @@
     "jquery": "1.10.2",
     "normalize-scss": "~2.1.2",
     "modernizr": "~2.7.1",
-    "requirejs": "~2.1.9",
-    <% if (cssPreprocessor === 'Sass') { %>
-    "sass-mixins": "~0.6.0"
-    <% } %>
-    <% if (cssPreprocessor === 'Less') { %>
-    "lesshat": "~2.0.0"
-    <% } %>
+    "requirejs": "~2.1.9"<% if (cssPreprocessor === 'Sass') { %>,
+    "sass-mixins": "~0.6.0"<% } else if (cssPreprocessor === 'Less') { %>,
+    "lesshat": "~2.0.0"<% } %>
   }
 }