Update chunky_png dependency to version 1.2.1
Update chunky_png dependency to version 1.2.1

flores/travis-ci,fxposter/travis-ci,fxposter/travis-ci,flores/travis-ci,openeducation/travis-ci,fxposter/travis-ci,flores/travis-ci,openeducation/travis-ci,openeducation/travis-ci