[#448] Fix brakeman run raising error on CI.

[htoo-eain-lwin]

close #448

What happened 👀

Having the following error using brakeman.run in Dangerfile causing error on CI.

danger-brakeman_scanner-0.1.1/lib/danger_plugin.rb:18:in `dirname':  (Danger::DSLError)
[!] Invalid `Dangerfile` file: no implicit conversion of nil into String
 #  from Dangerfile:7
 #  -------------------------------------------
 #  # Runs Brakeman on modified and added files
 >  brakeman.run
 #  

/danger-brakeman_scanner-0.1.1/lib/danger_plugin.rb:18:in `dirname': no implicit conversion of nil into String (TypeError)

  def run(options = File.dirname(Kernel.caller_locations.first.absolute_path))

Insight 📝

I try to run with brakeman.run('.') and brakeman.run('/.'). Both are working fine.

Proof Of Work 📹

This is the test repo using our template only with brakeman.run. The CI is failing with the brakeman error.
Here's the Action and here's the PR

This is with brakeman.run('./')
Here's Action and PR

[malparty]

OMG it was that simple ><
Thanks! Our project will directly benefit from it 🚀