Updated do_install_this() to unlink the .version file if it exists.  This
allows installed_perls() to recognize that do_install_this() changed the
version.

ref: https://github.com/gugod/App-perlbrew/issues/410
Merge remote-tracking branch 'upstream/develop' into issues-410
Merge pull request #413 from elderling/issues-410

Updated do_install_this() to unlink the .version file if it exists.