Update kerl

* Let get_active_path to use $REBAR_PLT_DIR for the current active installation path
Update kerl

* Define $_KERL_ACTIVE_DIR when activating
* Use $_KERL_ACTIVE_DIR for `kerl status`
Merge pull request #60 from jj1bdx/jj1bdx-active-path-fix

Update kerl to use $_KERL_ACTIVE_DIR for get_active_path
Merge branch 'master' into jj1bdx-dev
Update kerl

* Change get_releases() to accept the new naming scheme of
  `otp_src_MAJOR.MINOR.PATCH.tar.gz`, where MAJOR, MINOR, PATCH
  are all decimal letters and some additional letters in
  `[-0-9A-Za-z_.]` (see OTP-11615 on otp_src_17.0-rc1.tar.gz)