travis: another attempt at multiple allowed failures

It looks like what Travis wants is a list of hashes, rather than a hash
with a list.

.travis.yml

@@ -37,9 +37,8 @@ matrix:
          OPTIONS="-DBUILD_CLAR=ON -DBUILD_EXAMPLES=OFF -DCMAKE_BUILD_TYPE=Debug"
      os: linux
  allow_failures:
-   env:
-     - COVERITY=1
-     - VALGRIND=1
+   - env: COVERITY=1
+   - env: VALGRIND=1
 
 install:
   - ./script/install-deps-${TRAVIS_OS_NAME}.sh