Add conditional dep on nats to restore compat with GHC < 7.10

Also tweak changelog for consistency

Author: hvr

changelog.md

@@ -4,12 +4,9 @@
 
   * Removed `alwaysSucceeds` and `always`, GHC's invariant checking primitives. (GHC #14324)
 
-  * Add `lengthTBQueue` to `Control.Concurrent.STM.TBQueue`.
+  * Add `lengthTBQueue` to `Control.Concurrent.STM.TBQueue`
 
-  * Switched `newTBQueue` and `newTBQueueIO` to accept `Natural` as
-    size. [#17](https://github.com/haskell/stm/pull/17)
-
-  * Dropped support for `base < 4.8`, due to above change.
+  * Switched `newTBQueue` and `newTBQueueIO` to accept `Natural` as size (gh-17)
 
 ----
 

stm.cabal

@@ -1,6 +1,8 @@
+cabal-version:  >=1.10
 name:           stm
 version:        2.5.0.0
 -- don't forget to update changelog.md file!
+
 license:        BSD3
 license-file:   LICENSE
 maintainer:     libraries@haskell.org
@@ -9,7 +11,6 @@ bug-reports:    https://github.com/haskell/stm/issues
 synopsis:       Software Transactional Memory
 category:       Concurrency
 build-type:     Simple
-cabal-version:  >=1.10
 tested-with:    GHC==8.6.*, GHC==8.4.*, GHC==8.2.*, GHC==8.0.*, GHC==7.10.*, GHC==7.8.*, GHC==7.6.*, GHC==7.4.*, GHC==7.2.*, GHC==7.0.*
 description:
     Software Transactional Memory, or STM, is an abstraction for
@@ -42,6 +43,9 @@ library
     if impl(ghc >= 7.9)
         other-extensions: Safe
 
+    if !impl(ghc >= 7.10)
+        build-depends: nats (>= 0.1.3 && < 0.3) || (>= 1 && < 1.2)
+
     build-depends:
         base  >= 4.3 && < 4.13,
         array >= 0.3 && < 0.6