Travis: use pypy from Xenial, add pypy3

Author: blueyed

.travis.yml

@@ -30,9 +30,11 @@ matrix:
 jobs:
   include:
     # Coverage tracking is slow with pypy, skip it.
-    - env: TOXENV=pypy PYTEST_NO_COVERAGE=1
-      python: 'pypy-5.4'
-      dist: trusty
+    - env: TOXENV=pypy-xdist PYTEST_NO_COVERAGE=1
+      python: 'pypy2.7-6.0'
+    - env: TOXENV=pypy3-xdist PYTEST_NO_COVERAGE=1
+      python: 'pypy3.5-6.0'
+
     - env: TOXENV=py34-xdist
       python: '3.4'
     - env: TOXENV=py35-xdist