update python versions in travis.yml file

Author: spderosso

.travis.yml

@@ -6,11 +6,11 @@ addons:
     - snapcraft
 python:
 - '2.7'
-- '3.3'
 - '3.4'
 - '3.5'
 - '3.6'
-- pypy-5.3.1
+- '3.7'
+- 'pypy3.5'
 env: LIBGIT2=~/libgit2/_install/ LD_LIBRARY_PATH=~/libgit2/_install/lib
 before_install: ./.travis.sh
 install: pip install -r requirements.txt .