Fix tox for Jython

.travis.yml

@@ -36,7 +36,7 @@ before_install:
 
 install:
   - pip install coveralls
-  - pip install tox-travis
+  - pip install tox==3.9.0 tox-travis
 
 script: tox
 

ci/before_install_jython.sh

@@ -5,7 +5,8 @@ INST_DIR=$HOME/jython/jython-${JYTHON##*:}
 if [ ! -d "$INST_DIR" ]; then
     JYTHON_JAR=$(${TRAVIS_BUILD_DIR}/ci/mvnget.sh "$JYTHON")
     java -jar ${JYTHON_JAR} -s -d "$INST_DIR"
-    $HOME/jython/bin/pip install --upgrade pip
+    "$INST_DIR"/bin/pip install --upgrade pip
 fi
+pip install --upgrade virtualenv==16.5.0
 mkdir -p $HOME/bin
 ln -s "$INST_DIR"/bin/jython $HOME/bin/