ci: Travis use newer PyPy (#10)

Author: blueyed

.travis.yml

@@ -19,9 +19,9 @@ jobs:
       env: TOXENV=py37-coverage
     - python: '3.8-dev'
       env: TOXENV=py38-coverage
-    - python: 'pypy2.7-6.0'
+    - python: 'pypy'
       env: TOXENV=pypy-coverage
-    - python: 'pypy3.5-6.0'
+    - python: 'pypy3'
       env: TOXENV=pypy3-coverage
     # Fails currently badly.
     # - python: '3.7'