Bump version to MINOR release 2.7.0
Bump version to MINOR release 2.7.0

Features:
* Add support for Developer Preview features under a new preview tag
* Add roomHint property to smart home response
* Adds types for 2FA in smart home request/responses

Fixes:
* Fix conv.data not set when init.data has changed issue
* Fix package.json to correct Node version >=6.13.0
* Add warning for using DeepLink

Other Changes:
* Update dependencies for security
* Change library development tooling

Change-Id: I370808e3a52564304cfc2cdd94c1866beb198ca1

actions-on-google/actions-on-google-nodejs,actions-on-google/actions-on-google-nodejs,actions-on-google/actions-on-google-nodejs