fix bundle install error

fix issue of bundle install error after slack-notifier upgraded. upgrade to 0.3.2

Gemfile.lock

@@ -644,7 +644,7 @@ DEPENDENCIES
   simplecov
   sinatra
   six
-  slack-notifier (~> 0.2.0)
+  slack-notifier (~> 0.3.2)
   slim
   spinach-rails
   spring (= 1.1.1)
@@ -662,4 +662,4 @@ DEPENDENCIES
   unicorn (~> 4.6.3)
   unicorn-worker-killer
   version_sorter
-  webmock
\ No newline at end of file
+  webmock