Remove allow-fails (#581)

Both are no longer needed: debian testing has Python 2.7.13 final now,
and wheels of numpy and scipy are available.

.travis.yml

@@ -58,8 +58,6 @@ matrix:
     - flake8
   allow_failures:
     - env: PYTHON=3.5 CPP=17 GCC=7
-    - env: PYTHON=2.7 CPP=14 GCC=6 # Temporary until python >2.7.13-rc1 migrates to debian testing
-    - env: PYTHON=3.6 CPP=14 CLANG # Temporary until binary wheels of numpy and scipy become available on brew Python 3.6
 cache:
   directories:
   - $HOME/.cache/pip