travis.yml: also test on GHC 7.10.

.travis.yml

@@ -5,6 +5,7 @@ env:
  - GHCVER=7.4.2
  - GHCVER=7.6.3
  - GHCVER=7.8.3
+ - GHCVER=7.10.1 
  - GHCVER=head
 
 # Note: the distinction between `before_install` and `install` is not important.
@@ -67,4 +68,5 @@ script:
 
 matrix:
   allow_failures:
+   - env: GHCVER=7.10.1  
    - env: GHCVER=head