Bump cancancan

Conservative bump to a newer version that fixes some deprecated syntax for Rails 5.x (eg #before_filter)

Gemfile

@@ -32,7 +32,7 @@ gem 'activerecord-postgresql-adapter'
 gem 'pg', '~> 0.21.0'
 
 gem 'acts_as_list', '0.9.19'
-gem 'cancancan', '~> 1.7.0'
+gem 'cancancan', '~> 1.15.0'
 gem 'ffaker'
 gem 'highline', '2.0.3' # Necessary for the install generator
 gem 'json'

Gemfile.lock

@@ -137,7 +137,7 @@ GEM
       activesupport (>= 3.0.0)
       uniform_notifier (~> 1.11)
     byebug (11.1.3)
-    cancancan (1.7.1)
+    cancancan (1.15.0)
     capybara (3.32.2)
       addressable
       mini_mime (>= 0.1.3)
@@ -608,7 +608,7 @@ DEPENDENCIES
   bugsnag
   bullet
   byebug
-  cancancan (~> 1.7.0)
+  cancancan (~> 1.15.0)
   capybara
   catalog!
   coffee-rails (~> 4.2.2)