Update changelog and bump version to 0.5.1.2

array.cabal

 name:          array
-version:       0.5.1.1
+version:       0.5.1.2
 -- NOTE: Don't forget to update ./changelog.md
 license:       BSD3
 license-file:  LICENSE

changelog.md

 # Changelog for [`array` package](http://hackage.haskell.org/package/array)
 
+## 0.5.1.2  *TBD*
+
+  * Bundled with GHC 8.2.1
+  * Overflow check in `unsafeNewArray`
+
 ## 0.5.1.1  *Apr 2016*
 
   * Bundled with GHC 8.0.1