WIP don't test older PyPy versions

Author: mgeier

.travis.yml

@@ -8,11 +8,8 @@ python:
   - "3.5"
   - "3.6"
   - "nightly"
-  - "pypy-5.3.1"
-  - "pypy-5.4.1"
-  # TODO: Enable pypy3 once NumPy is working there, see
-  # https://bitbucket.org/pypy/pypy/issues/1567/
-  #- "pypy3"
+  - "pypy2.7"
+  - "pypy3.5"
 addons:
   apt:
     packages: