Update sentry-raven to 0.15.6

Gemfile

@@ -218,7 +218,7 @@ gem 'virtus',             '~> 1.0.1'
 gem 'net-ssh',            '~> 3.0.1'
 
 # Sentry integration
-gem 'sentry-raven'
+gem 'sentry-raven', '~> 0.15'
 
 # Metrics
 group :metrics do

Gemfile.lock

@@ -722,7 +722,7 @@ GEM
       activesupport (>= 3.1, < 4.3)
     select2-rails (3.5.9.3)
       thor (~> 0.14)
-    sentry-raven (0.15.4)
+    sentry-raven (0.15.6)
       faraday (>= 0.7.6)
     settingslogic (2.0.9)
     sexp_processor (4.6.0)
@@ -1007,7 +1007,7 @@ DEPENDENCIES
   sdoc (~> 0.3.20)
   seed-fu (~> 2.3.5)
   select2-rails (~> 3.5.9)
-  sentry-raven
+  sentry-raven (~> 0.15)
   settingslogic (~> 2.0.9)
   sham_rack
   shoulda-matchers (~> 2.8.0)