After about 4 years of "on and off" searching for a solution to this, I do not believe this is possible as the UIWebView
will not allow you to set the keyboard submit text via JavaScript or an HTML attribute. So this would require the use of <textInputTraits key="textInputTraits" returnKeyType="Send"/>
within a storyboard, or programatically through the view controller which doesn't solve the problem for cordova.
The Ionic Keyboard Plugin for Cordova have also not cracked this fairly popular request since the issue was opened Dec 2014.
Note: You can add <button type="submit">Whatever</button>
below your textfield to at least allow the keyboard to display the blue "Go" button which submits the form.