Fixes to the Travis build. (#1111)

These fixes were originally implemented by user tbbharaj in #1108.
Extracting them into their own PR since 1108 is still being worked and I'd very much like to benefit from this
work across _all_ PRs against python-driver.

Major thanks to tbbharaj for the original work here.

Author: absurdfarce

.travis.yml

@@ -24,6 +24,7 @@ addons:
     - libev-dev
 
 install:
+  - pip install --upgrade setuptools
   - pip install tox-travis
   - if [[ $TRAVIS_PYTHON_VERSION != pypy3.5 ]]; then pip install lz4; fi
 

tox.ini

@@ -12,6 +12,7 @@ deps = nose
        pure-sasl
        kerberos
        futurist
+       greenlet>=0.4.14,<0.4.17
 lz4_dependency = py27,py35,py36,py37,py38: lz4
 
 [testenv]