Remove python 3.5 support; add python 3.8 support

- Python 3.5 has reached end-of-life.
- Add support for Python 3.8
- Move dist to bionic (xenial is EOL in April)
- Upgrade pip in travis.yml's `before_install`. this should install a wheel
  for pyca/cryptography
- Install rust for pypy builds. It is a requirement for cryptography as no
  pypy wheels exist.

1 files changed, 1 insertions, 1 deletions

diff --git a/README.rst b/README.rst
index 0b42133..56e41c1 100644
--- a/README.rst
+++ b/README.rst
@@ -2,7 +2,7 @@ OAuthLib - Python Framework for OAuth1 & OAuth2
 ===============================================
 
 *A generic, spec-compliant, thorough implementation of the OAuth request-signing
-logic for Python 3.5+.
+logic for Python 3.6+.
 
 .. image:: https://travis-ci.org/oauthlib/oauthlib.svg?branch=master
   :target: https://travis-ci.org/oauthlib/oauthlib