Upgrade fog-aws to v3.12.0

This upgrade properly supports regional STS endpoints as well as the
ability to set the minimum and maximum multipart chunk size.

Diff:
https://github.com/fog/fog-aws/compare/v3.9.0..v3.12.0

Changelog: fixed

Gemfile

@@ -120,7 +120,7 @@ gem 'carrierwave', '~> 1.3'
 gem 'mini_magick', '~> 4.10.1'
 
 # for backups
-gem 'fog-aws', '~> 3.9'
+gem 'fog-aws', '~> 3.12'
 # Locked until fog-google resolves https://github.com/fog/fog-google/issues/421.
 # Also see config/initializers/fog_core_patch.rb.
 gem 'fog-core', '= 2.1.0'

Gemfile.lock

@@ -395,7 +395,7 @@ GEM
       fog-json
       ipaddress (~> 0.8)
       xml-simple (~> 1.1)
-    fog-aws (3.9.0)
+    fog-aws (3.12.0)
       fog-core (~> 2.1)
       fog-json (~> 1.1)
       fog-xml (~> 0.1)
@@ -1452,7 +1452,7 @@ DEPENDENCIES
   flipper-active_support_cache_store (~> 0.21.0)
   flowdock (~> 0.7)
   fog-aliyun (~> 0.3)
-  fog-aws (~> 3.9)
+  fog-aws (~> 3.12)
   fog-core (= 2.1.0)
   fog-google (~> 1.15)
   fog-local (~> 0.6)