Remove the Download cache timeout

This commit removes the timeout limit for the download cache, instead
falling back to the Ruby default of 60 seconds.

[#83473194]
Merge branch 'cgfrost-master'

[resolves #113]
Merge remote-tracking branch 'upstream/master'

Conflicts:
	lib/java_buildpack/util/cache/download_cache.rb
	spec/java_buildpack/util/cache/download_cache_spec.rb