Update incorrect Google API key help text (#3595)

* Update Youtube API key help text

* Update en.json

webapp/components/admin_console/external_service_settings.jsx

@@ -77,7 +77,7 @@ export default class ExternalServiceSettings extends AdminSettings {
                     helpText={
                         <FormattedHTMLMessage
                             id='admin.service.googleDescription'
-                            defaultMessage='Set this key to enable embedding of YouTube video previews based on hyperlinks appearing in messages or comments. Instructions to obtain a key available at <a href="https://www.youtube.com/watch?v=Im69kzhpR3I" target="_blank">https://www.youtube.com/watch?v=Im69kzhpR3I</a>. Leaving the field blank disables the automatic generation of YouTube video previews from links.'
+                            defaultMessage='Set this key to enable the display of titles for embedded YouTube video previews. Without the key, YouTube previews will still be created based on hyperlinks appearing in messages or comments but they will not show the video title. View a <a href="https://www.youtube.com/watch?v=Im69kzhpR3I" target="_blank">Google Developers Tutorial</a> for instructions on how to obtain a key.'
                         />
                     }
                     value={this.state.googleDeveloperKey}