Change 'Insert image' text to 'Insert image URL'

Author: JavierGelatti

vendor/assets/javascripts/bootstrap-wysihtml5/core-b3.js.erb

@@ -496,7 +496,7 @@
                 target: "Open link in new window"
             },
             image: {
-                insert: "Insert image",
+                insert: "Insert image URL",
                 cancel: "Cancel"
             },
             html: {