Merge pull request #36 from qiniu/develop

make travis-ci ok
Merge pull request #43 from qiniu/develop

imageMogr bugfix: auto-orient
Merge pull request #46 from qiniu/develop

update docs v2.4.2
Merge pull request #48 from qiniu/develop

remove auth.GetPolicy.scope default value
fix version number
Merge pull request #50 from why404/hotfix/v2.4.2

Hotfix/v2.4.2