Bump Digits twitter-core dependency from 1.4.+ to 1.6.+
Bump Digits twitter-core dependency from 1.4.+ to 1.6.+

Change-Id: I32f9d155664ac307138fcf04723b2f547af00f59

dejavu1988/digits-android,jaydeep17/digits-android,dejavu1988/digits-android,jaydeep17/digits-android,twitter/digits-android,twitter/digits-android