[MaterialInk] Make sure completion block is fired after ink animation completes
[MaterialInk] Make sure completion block is fired after ink animation completes

Summary:
[MaterialInk] Make sure completion block is fired after ink animation completes

Make sure completion block is fired after ink animation completes.

Closes https://github.com/google/material-components-ios/issues/72

Reviewers: featherless, ajsecord, #material_components_ios_owners, randallli

Reviewed By: #material_components_ios_owners, randallli

Subscribers: ajsecord

Projects: #material_components_ios

Differential Revision: http://codereview.cc/D109

sigito/material-components-ios,brianjmoore/material-components-ios,material-components/material-components-ios,chriscox/material-components-ios,brianjmoore/material-components-ios,material-components/material-components-ios,sigito/material-components-ios,samnm/material-components-ios,brianjmoore/material-components-ios,material-components/material-components-ios,material-components/material-components-ios,chriscox/material-components-ios,willlarche/material-components-ios,samnm/material-components-ios,sigito/material-components-ios,samnm/material-components-ios,samnm/material-components-ios,randallli/material-components-ios,randallli/material-components-ios,chriscox/material-components-ios,Eccelor/material-components-ios,randallli/material-components-ios,material-components/material-components-ios,willlarche/material-components-ios,Eccelor/material-components-ios,sigito/material-components-ios,Eccelor/material-components-ios,willlarche/material-components-ios,brianjmoore/material-components-ios,randallli/material-components-ios,chriscox/material-components-ios,Eccelor/material-components-ios,sigito/material-components-ios,brianjmoore/material-components-ios,chriscox/material-components-ios,Eccelor/material-components-ios,willlarche/material-components-ios,randallli/material-components-ios,willlarche/material-components-ios,samnm/material-components-ios,randallli/material-components-ios