bump to 3.1.1 for Xcode 9.3

bump to 3.1.1 for Xcode 9.3

bump to 3.1 release (ChartsOrg#3357)

bump pod version

Update README.md

bump version

Merge pull request ChartsOrg#2301 from simonbromberg/master

Minor typo fix in console alert message "it's" -> "its"

3.0.1 release

release 2.3.1

3.0.0 release