Update jnr-ffi dependency version

A recent commit seems to have bumped the version number of the
jnr-posix dependency, which has a transitive dependency on
jnr-ffi 1.0.10.  However, the jruby-core pom still specifies
an explicit dependency on 1.0.7.  This updates it to 1.0.10.
Merge pull request #1939 from cprice404/maint/jruby-1_7/fix-jnr-ffi-dep-ver

Update jnr-ffi dependency version