Upgrade jar-tool to 0.1.7

This picks up a fix that prevented clean cross-fs
jar copies due to unclosed temprorary files.

Testing Done:
# observed jar-tool 0.1.7 ivy download and subsequent jarring (not cross-fs) work:
$ PANTS_DEV=1 ./pants goal clean-all killserver server
$ PANTS_DEV=1 ./pants goal binary bundle src/{java,scala}/::

Bugs closed: 198

Reviewed at https://rbcommons.com/s/twitter/r/475/