Adding hideSoftKeyboard functionality  for android, updating package.json and updating ...

- Adding hiding soft keyboard for android. It checks whether soft keyboard is present using `adb dumpsys input_method` , if true hides keyboard using back button else throws an error.
- Updated package.json and submodule/appium-adb to new version of appium-adb
- Issue #2021
I'm not sure it makes sense for hideKeyboard to error. In test the client side test code I want to do this:

```ruby
first_textfield.send_keys 'some text'
hide_keyboard # maybe it's there and maybe not. either way I don't want an error
```