application.resetPassword clears custom user data

[brussellc5]

Reproduced in branch 2.0.1-okta

Steps to reproduce:
Create a user with any custom data
Use application.resetPassword
Note that all custom data has been cleared from the user account

The problem seems to stem from the DefaultDataStore.save method defined on line 445 of impl.ds.DefaultDataStore:
476: // if this is an Okta CRUD operation, we must use a PUT and not a POST

The docs state that a POST shuld be used to perform a partial update, not a PUT:
https://developer.okta.com/docs/api/resources/users.html#update-user

[brussellc5]

See #1354