Make the JRubyExec `script` argument optional provided `jrubyArgs` is set

Fixes #62
Merge pull request #63 from rtyler/62-optional-script-jrubyexec

Make the JRubyExec `script` argument optional provided `jrubyArgs` is present
An update to @rtyler's commit that looks for -S in jrubyArgs of JRubyExec.
Fixed failing unittests for project.jrubyexec. Updated README.
Removed dead code
Merge pull request #64 from ysb33r/master

Updates to JRubyExec & project.jrubyexec to handle '-S'
Revert back to 1.7.15 as the default

See <https://github.com/jruby/jruby/issues/2032>
Update the changelog with the 0.1.3 milestone
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