Merge branch 'master' of https://github.com/aFarkas/lazysizes into gh…

…-pages

# Conflicts:
#	lazysizes-umd.min.js
#	lazysizes.min.js
#	plugins/artdirect/ls.artdirect.min.js
#	plugins/attrchange/ls.attrchange.min.js
#	plugins/blur-up/ls.blur-up.min.js
#	plugins/object-fit/ls.object-fit.min.js
#	plugins/optimumx/ls.optimumx.min.js
#	plugins/parent-fit/ls.parent-fit.min.js
#	plugins/respimg/ls.respimg.min.js
#	plugins/twitter/ls.twitter.min.js
#	plugins/video-embed/ls.video-embed.min.js