monaco_editor: configure prettier to not add trailing comas

jslint complain about trailing commas

bt5/erp5_monaco_editor/SkinTemplateItem/portal_skins/erp5_monaco_editor/monaco-editor.gadget.js.js

@@ -145,6 +145,7 @@
                   // see http://json.schemastore.org/prettierrc for supported options.
                   singleQuote: true,
                   tabWidth: 2,
+                  trailingComma: 'none'
                 });
 
                 return [

bt5/erp5_monaco_editor/SkinTemplateItem/portal_skins/erp5_monaco_editor/monaco_editor_support.zpt

@@ -153,7 +153,8 @@ $script.onload = function() {
         plugins: [prettierPlugins.babel],
         // see http://json.schemastore.org/prettierrc for supported options.
         singleQuote: true,
-        tabWidth: 2
+        tabWidth: 2,
+        trailingComma: 'none'
       });
 
       return [