Use newer PyPy

https://docs.travis-ci.com/user/languages/python/#PyPy-Support

Because current pypy 2.5.0 builds are too slow
https://travis-ci.org/sdg-mit/gitless/builds/213701497

Author: techtonik

.travis.yml

@@ -6,7 +6,7 @@ python:
   - "3.3"
   - "3.4"
   - "3.5"
-  - "pypy"
+  - "pypy-5.3.1"
 
 env: LIBGIT2=~/libgit2/_install/ LD_LIBRARY_PATH=~/libgit2/_install/lib