Bump to 1.1.15 and closure-compiler-2020-06-28

[hmdne]

No description provided.

[yogs174]

Thanks @hmdne Your updated code helped me to work with latest node packages.

[Radagaisus]

@knowtheory Is this gem still maintained?

[hmdne]

I now build a Gem named closure-compiler-updated from https://github.com/hmdne/closure-compiler-updated . I can offer to help maintain this project if a need arises but if not, I maintain the fork.