Merge branch 'hotfix/v0.2.1'
Merge branch 'release/v0.2.2'
Merge branch 'release/v0.2.3'
Merge branch 'release/v0.2.4'
Merge branch 'release/v0.2.5'
Update README.md
Merge branch 'develop'
Fix a bug when including node-gcm-service@0.2.6