Prepend the user's PATH with the right PATH for the gem configuration in JRubyExec

Fixes #68, #70
Refactor the PATH computation to be a bit more testable
Merge pull request #72 from rtyler/jrubyexec-path-fixes

Jrubyexec path fixes
Bump the integration tests to check for temple-0.6.10 which is a transitive dep of slim

The real fix will come later when we stop checking specific versions of gems on
the file systems
Bump to the next release version
Use the appropriate gemDir when setting the PATH env variable

Fixes #70