travis: use LLVM 3.7

Signed-off-by: Austin Seipp <austin@well-typed.com>

.travis.yml

@@ -12,17 +12,17 @@ addons:
   apt:
     sources:
     - hvr-ghc
-    - llvm-toolchain-precise-3.6
+    - llvm-toolchain-precise-3.7
     - ubuntu-toolchain-r-test
     packages:
     - cabal-install-1.18
     - ghc-7.8.4
     - alex-3.1.3
     - happy-1.19.4
-    - llvm-3.6
+    - llvm-3.7
 
 before_install:
- - export PATH=/opt/ghc/7.8.4/bin:/opt/cabal/1.18/bin:/opt/alex/3.1.3/bin:/opt/happy/1.19.4/bin:/usr/lib/llvm-3.6/bin:$PATH
+ - export PATH=/opt/ghc/7.8.4/bin:/opt/cabal/1.18/bin:/opt/alex/3.1.3/bin:/opt/happy/1.19.4/bin:/usr/lib/llvm-3.7/bin:$PATH
 
 # Be explicit about which protocol to use, such that we don't have to repeat the rewrite command for each.
  - git config remote.origin.url git://github.com/${TRAVIS_REPO_SLUG}.git