In order to fix this problem just create API key from Google by going to Google Developer API page and put key in file "config.json" located in builder web root folder — you need to set it to parameter "googleFontsApiKey".
Note: Sometimes, the Google Maps widget also may not work in your builder. To resolve this, do the same as for Google Fonts but use this link for key creation and parameter "googleMapsApiKey" in file "config.json".