Change License to ASLv2 or MIT

[frotsch]

Would like to see this project gets relicensed under Apache 2 or MIT to make usage of this library easier from a compliance/legal view.

[thll]

With this now being a dependency of the Amazon Kinesis Client version 3.x, is there a chance that the license gets updated any time soon?

[awelless]

@frotsch @thll The license has been changed to Apache License 2.0 in the the 1.4.0 release of the library.