fix(Rakefile) Remove -d32 as argument to closure-compiler

[kimpettersen]

Closes #1765

[benmccann]

If you're interested in building with closure compiler then you might like this change I made which fixes tons of warnings:
#1710

[pkozlowski-opensource]

@kimpettersen thank you for your contribution but the -d32 flag makes the whole process run 2x faster which is important for the build. On top of this we've got another PR #1719 that removes this flag conditionally so going to close this one.