Re-enable failures for linux and OSX travis builds. (#1817)

.travis.yml

@@ -33,9 +33,6 @@ matrix:
           sources: ubuntu-toolchain-r-test
           packages: ninja-build g++-5
       env: DXC_BUILD_TYPE=Release
-  allow_failures:
-    - os: linux
-    - os: osx
 
 cache:
   apt: true