Add .css ext for non-SASS file part 2

Author: fbacall

app/assets/stylesheets/application.scss

@@ -50,7 +50,7 @@
 @import "bootstrap-datetimepicker.css";
 @import "ardc_vocab_widget_v2";
 @import "jquery.qtip.min";
-@import "select2";
+@import "select2.css";
 @import "select2-bootstrap-theme";
 @import "simple_calendar";
 @import "ol-geocoder";