Bump to 3.1.2

Also, 3.1.0 and 3.1.1 will be yanked because of the regression.

Gemfile.lock

 PATH
   remote: .
   specs:
-    paperclip (3.1.1)
+    paperclip (3.1.2)
       activemodel (>= 3.0.0)
       activerecord (>= 3.0.0)
       activesupport (>= 3.0.0)

NEWS

+New in 3.1.2:
+
+* Bug fix: #remove_attachment on 3.1.0 and 3.1.1 mistakenly trying to remove the column that has
+  the same name as data type (such as :string, :datetime, :interger.) You're advised to update to
+  Paperclip 3.1.2 as soon as possible.
+
 New in 3.1.1:
 
 * Bug fix: Paperclip will only load Paperclip::Schema only when Active Record is available.

lib/paperclip/version.rb

 module Paperclip
-  VERSION = "3.1.1" unless defined? Paperclip::VERSION
+  VERSION = "3.1.2" unless defined? Paperclip::VERSION
 end