Get rid of hard coded new branch

app/assets/javascripts/gl_dropdown.js

@@ -30,7 +30,7 @@ GitLabDropdownInput = (function() {
       }
     })
     .on('input', function(e) {
-      var val = e.currentTarget.value || 'new-branch';
+      var val = e.currentTarget.value || _this.options.inputFieldName;
       val = val.split(' ').join('-') // replaces space with dash
         .replace(/[^a-zA-Z0-9 -]/g, '').toLowerCase() // replace non alphanumeric
         .replace(/(-)\1+/g, '-'); // replace repeated dashes

app/assets/javascripts/project.js

@@ -85,6 +85,7 @@ import Cookies from 'js-cookie';
           filterable: true,
           filterRemote: true,
           filterByText: true,
+          inputFieldName: $dropdown.data('input-field-name'),
           fieldName: $dropdown.data('field-name'),
           renderRow: function(ref) {
             var li = refListItem.cloneNode(false);