Fix: Travis pypy test environment fails to install

.travis.yml

@@ -6,8 +6,6 @@ matrix:
   include:
     - python: pypy3
       env: TOX_ENV=pypy
-      before_install:
-      - python -m pip install --upgrade virtualenv
     - python: 3.5
       env: TOX_ENV=py35
     - python: 3.6
@@ -27,9 +25,6 @@ matrix:
     - python: 3.9
       env: TOX_ENV=verify-manifest
 
-before_install:
-  - python -m pip install --upgrade virtualenv
-
 install:
   - pip install tox
   - pip install python-coveralls

tox.ini

@@ -8,6 +8,7 @@ envlist = py35, py36, py37, py38, py39, pypy, flake8, pylint-errors, pylint-full
 
 [testenv]
 commands = nosetests --with-timer
+install_command = pip install --prefer-binary {opts} {packages}
 
 deps =
     nose