Update slack to fix issues with ruby 1.9.3

Gemfile

@@ -131,7 +131,7 @@ gem "gitlab-flowdock-git-hook", "~> 0.4.2"
 gem "gemnasium-gitlab-service", "~> 0.2"
 
 # Slack integration
-gem "slack-notifier", "~> 0.2.0"
+gem "slack-notifier", "~> 0.3.2"
 
 # d3
 gem "d3_rails", "~> 3.1.4"