Downgrade coverage dependency for Jython runs as Jython doesn't seem to have sqlite3 lib

.travis.yml

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

ci/before_install_jython.sh

@@ -6,6 +6,6 @@ if [ ! -d "$INST_DIR" ]; then
     JYTHON_JAR=$(${TRAVIS_BUILD_DIR}/ci/mvnget.sh "$JYTHON")
     java -jar ${JYTHON_JAR} -s -d "$INST_DIR"
 fi
-pip install --upgrade virtualenv==15.0.1
+pip install --upgrade virtualenv==15.0.1 tox==3.9.0 coverage==4.5.4
 mkdir -p $HOME/bin
 ln -s "$INST_DIR"/bin/jython $HOME/bin/