set texttemplate dflt back to ''

Author: antoinerg

src/plots/texttemplate_attributes.js

@@ -32,6 +32,7 @@ module.exports = function(opts, extra) {
     var texttemplate = {
         valType: 'string',
         role: 'info',
+        dflt: '',
         editType: opts.editType || 'calc',
         description: [
             'Template string used for rendering the information text that appear on points.',