remove extra spaces for src descriptions

Author: archmoj

src/plot_api/plot_schema.js

@@ -603,10 +603,7 @@ function mergeValTypeAndRole(attrs) {
     function makeSrcAttr(attrName) {
         return {
             valType: 'string',
-            description: [
-                'Sets the source reference on Chart Studio Cloud for ',
-                attrName, '.'
-            ].join(' '),
+            description: 'Sets the source reference on Chart Studio Cloud for ' + attrName + '.',
             editType: 'none'
         };
     }