Fix chainer and protobuf versions on travis because they release incompatible versions to Python2

- chainer/chainer#8545
- protocolbuffers/protobuf#8984

Author: pazeshun

.travis.yml

@@ -88,6 +88,7 @@ before_script:
   - find $HOME/.cache/pip -type f
   - export ROSDEP_ADDITIONAL_OPTIONS='-n -v --ignore-src' # run rosdep without -q, -r and -v
   - if [ ${ROS_DISTRO} == "hydro" ]; then export BEFORE_SCRIPT="sed -ie \"/-pip/ d\" \${CI_SOURCE_PATH}/package.xml;${BEFORE_SCRIPT}"; fi # FIXME hydro does not have python >= 2.7.9, so it fails on pip install
+  - if [ ${ROS_DISTRO} != "hydro" ]; then export BEFORE_SCRIPT="sudo -H pip install chainer==6.7.0 protobuf==3.17.3;${BEFORE_SCRIPT}"; fi # FIXME chainer and protobuf release incompatible versions to Python2 (https://github.com/chainer/chainer/issues/8545, https://github.com/protocolbuffers/protobuf/issues/8984)
   - if [ ${ROS_DISTRO} == "noetic" ]; then export BEFORE_SCRIPT="sed -ie \"/gazebo/ d\" \${CI_SOURCE_PATH}/package.xml;${BEFORE_SCRIPT}"; fi # FIXME gazebo is not released in noetic
   - if [ ${ROS_DISTRO} == "noetic" ]; then export BEFORE_SCRIPT="touch ros_tutorials/turtlesim/CATKIN_IGNORE; ${BEFORE_SCRIPT}"; fi # qt5/moc does not work on docker (https://stackoverflow.com/questions/56319830/error-when-building-qt-app-in-a-recent-docker)
   - mkdir .travis; mv *.sh *.py *.conf .travis/ # need to move, since directory starting from . is ignoreed by catkin build