Temporarily pin virtualenv to 16.7.10 to fix CI failures

.github/workflows/test.yml

@@ -40,7 +40,7 @@ jobs:
         python-version: ${{ matrix.python }}
         architecture: ${{ matrix.arch }}
     - name: install tox
-      run: pip install --upgrade 'setuptools!=50' 'virtualenv<20' tox==3.20.1
+      run: pip install --upgrade 'setuptools!=50' 'virtualenv<16.7.11' tox==3.20.1
     - name: setup tox environment
       run: tox -e ${{ matrix.toxenv }} --notest
     - name: test

.travis.yml

@@ -85,7 +85,7 @@ jobs:
 install:
 # pip 21.0 no longer works on Python 3.5
 - pip install -U pip==20.3.4 setuptools
-- pip install -U 'virtualenv<20'
+- pip install -U 'virtualenv<16.7.11'
 - pip install -U tox==3.20.1
 - python2 -m pip install --user -U typing
 - tox --notest

test-requirements.txt

@@ -12,6 +12,6 @@ pytest-forked>=1.3.0,<2.0.0
 pytest-cov>=2.10.0,<3.0.0
 typing>=3.5.2; python_version < '3.5'
 py>=1.5.2
-virtualenv<20
+virtualenv<16.7.11
 setuptools!=50
 importlib-metadata==0.20