Fix issue with edit icons.

app/javascript/css/edit.scss

@@ -81,7 +81,7 @@
 }
 
 .wmd-button > span {
-    background-image: image-url("../images/wmd-buttons.png");
+    background-image: url("../images/wmd-buttons.png");
     background-repeat: no-repeat;
     background-position: 0px 0px;
     width: 20px;