Revert Animator callback fixed (leandroBorgesFerreira#139)

Fix 134 (leandroBorgesFerreira#138)

* fixing visibility GONE bug

* version bump

Merge pull request leandroBorgesFerreira#112 from leandroBorgesFerrei…

…ra/set_progress_error_message

improving error message

Merge pull request leandroBorgesFerreira#103 from leandroBorgesFerrei…

…ra/getState

adding method to getState

Merge pull request leandroBorgesFerreira#100 from leandroBorgesFerrei…

…ra/open_classes

making buttons extensibles

Merge pull request leandroBorgesFerreira#98 from leandroBorgesFerreir…

…a/wait_to_stop

never begin progress if stop was called before morph finishes

Merge pull request leandroBorgesFerreira#97 from leandroBorgesFerreir…

…a/min_api_16

minSdkVersion 16

Update README.md

Merge pull request leandroBorgesFerreira#92 from leandroBorgesFerreir…

…a/determinate_progress

Determinate progress

Merge pull request leandroBorgesFerreira#91 from leandroBorgesFerreir…

…a/version2_refactor

Version 2.0.0