require virtualenv<14.0 so we get a py32 compatible pip

.travis/install.sh

@@ -36,9 +36,9 @@ if [[ "$(uname -s)" == 'Darwin' ]]; then
             ;;
     esac
     pyenv rehash
-    python -m pip install --user virtualenv
+    python -m pip install --user 'virtualenv<14.0'
 else
-    pip install virtualenv
+    pip install 'virtualenv<14.0'
     sudo add-apt-repository -y ppa:gezakovacs/lz4
     sudo apt-get update
     sudo apt-get install -y liblz4-dev