make bootstrap-sass-official dependency exclusive to sass option

Author: DaftMonk

app/templates/_bower.json

@@ -5,8 +5,8 @@
     "angular": ">=1.2.*",
     "json3": "~3.3.1",
     "es5-shim": "~3.0.1",
-    "jquery": "~1.11.0",<% if(filters.bootstrap) { %>
-    "bootstrap-sass-official": "~3.1.1",
+    "jquery": "~1.11.0",<% if(filters.bootstrap) { %><% if (filters.sass) { %>
+    "bootstrap-sass-official": "~3.1.1",<% } %>
     "bootstrap": "~3.1.1",<% } %>
     "angular-resource": ">=1.2.*",
     "angular-cookies": ">=1.2.*",