chore(build): prepare for 5.2.1 release

FineUploader#1398

chore(release): prepare for 5.2.0 release

test(firefox): try to fix weird test failure in FF

FineUploader#1345

chore(release): prepare for 5.1.2 release

chore: increment version

due to my error on first npm publish... starting the new year right!

chore(build): prepare for 5.0.9 release

chore(build): prepare for 5.0.8 release

chore(release): prepare for 5.0.7 release

chore(build): 5.0.6 release

chore($build): 5.0.5 release

[skip ci]