Log Message:
p5-ack: update to 2.18.

2.18    Fri Mar 24 14:53:19 CDT 2017
====================================
ack 2.18 will probably be the final release in the ack 2.x series.
I'm going to be starting work on ack 3.000 in earnest.  Still,
if you discover problems with ack 2, please report them to
https://github.com/petdance/ack2/issues

If you're interested in ack 3 development, please sign up
for the ack-dev mailing list and/or join the ack Slack.  See
https://beyondgrep.com/community/ for details.

[INTERNALS]
Removed the abstraction of App::Ack::Resource and its subclass
App::Ack::Resource::Basic.  We are abandoning the idea that we'll have
plugins.

2.17_02 Thu Mar 23 22:25:13 CDT 2017
====================================
[FIXES]
ack no longer throws an undefined variable warning if it's called
from a directory that doesn't exist. (GH #634)

[DOCUMENTATION]
Explain that filetypes must be two characters or longer. (GH #389)

[INTERNALS]
Removed dependency on File::Glob which isn't used.