NXD: get mimemagic from github

mimemagic was yanked from rubygems, so this cause gitlab to fail building. To
make it possible to keep installing this old version of gitlab we get mimemagic
from git.

Gemfile

@@ -190,6 +190,7 @@ gem 'gitlab-flowdock-git-hook', '~> 1.0.1'
 
 # Gemnasium integration
 gem "gemnasium-gitlab-service", git: "https://github.com/gemnasium/gemnasium-gitlab-service"
+gem "mimemagic", git: "https://github.com/mimemagicrb/mimemagic"
 
 # Slack integration
 gem 'slack-notifier', '~> 1.5.1'

Gemfile.lock

@@ -5,6 +5,12 @@ GIT
     gemnasium-gitlab-service (0.2.6)
       rugged (~> 0.21)
 
+GIT
+  remote: https://github.com/mimemagicrb/mimemagic
+  revision: a4b038c6c1b9d76dac33d5711d28aaa9b4c42c66
+  specs:
+    mimemagic (0.3.0)
+
 GEM
   remote: https://rubygems.org/
   specs:
@@ -1026,6 +1032,7 @@ DEPENDENCIES
   foreman (~> 0.78.0)
   fuubar (~> 2.2.0)
   gemnasium-gitlab-service!
+  mimemagic!
   gemojione (~> 3.3)
   gettext (~> 3.2.2)
   gettext_i18n_rails (~> 1.8.0)