Travis-CI: update the list of Ruby's and Python's versions

Travis-CI no longer provides Ruby 2.0 in its Trusty environment (it has
been updated according to
https://blog.travis-ci.com/2017-06-21-trusty-updates-2017-Q2-launch).
Remove this version from .travis.yml.

Moreover Python 3.6 and Ruby 3.4 are available. Test building with them.

Last by not least, pypy virtual environment directory has been renamed
pypy2 (/home/travis/virtualenv/pypy2 is a symbolic link to pypy2-5.6.0).

The updated .travis.yml file has been tested on
https://travis-ci.org/fishilico/selinux/builds/248126824

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>

.travis.yml

@@ -11,21 +11,22 @@ compiler:
 env:
   matrix:
     # Test the last version of Python and Ruby together, with some linkers
-    - PYVER=python3.5 RUBYLIBVER=2.3
-    - PYVER=python3.5 RUBYLIBVER=2.3 LINKER=gold
-    - PYVER=python3.5 RUBYLIBVER=2.3 LINKER=bfd
+    - PYVER=python3.6 RUBYLIBVER=2.4
+    - PYVER=python3.6 RUBYLIBVER=2.4 LINKER=gold
+    - PYVER=python3.6 RUBYLIBVER=2.4 LINKER=bfd
 
     # Test several Python versions
-    - PYVER=python2.7 RUBYLIBVER=2.3
-    - PYVER=python3.3 RUBYLIBVER=2.3
-    - PYVER=python3.4 RUBYLIBVER=2.3
-    - PYVER=pypy RUBYLIBVER=2.3
+    - PYVER=python2.7 RUBYLIBVER=2.4
+    - PYVER=python3.3 RUBYLIBVER=2.4
+    - PYVER=python3.4 RUBYLIBVER=2.4
+    - PYVER=python3.5 RUBYLIBVER=2.4
+    - PYVER=pypy2 RUBYLIBVER=2.4
     #- PYVER=pypy3 RUBYLIBVER=2.3 # PyPy3 5.5.0 provides the Python2 form of some structures, which makes it incompatible with SWIG
 
     # Test several Ruby versions
-    - PYVER=python3.5 RUBYLIBVER=2.0
-    - PYVER=python3.5 RUBYLIBVER=2.1
-    - PYVER=python3.5 RUBYLIBVER=2.2
+    - PYVER=python3.6 RUBYLIBVER=2.1
+    - PYVER=python3.6 RUBYLIBVER=2.2
+    - PYVER=python3.6 RUBYLIBVER=2.3
 
 # Use Travis-CI Ubuntu 14.04 Trusty infrastructure
 sudo: required