set version to 2.1.0 for release

bump version to 2.0.0

bump version to 1.7.1

Merge pull request sailthru#56 from sailthru/purchase_channel

Add channel, app_id, and device_id to purchases

bump version to 1.6.0

[maven-release-plugin] copy for tag sailthru-java-client-1.3.3

[maven-release-plugin] copy for tag sailthru-java-client-1.3.2

[maven-release-plugin] copy for tag sailthru-java-client-1.3.1

[maven-release-plugin] copy for tag sailthru-java-client-1.3.0