use ros-infrastructure/rosdep#694 to respect version_lt for python pi…

…p, some package requries python3

.travis.yml

@@ -30,6 +30,8 @@ before_script:
   - if [[ "$ROS_DISTRO" == "kinetic" && "$DOCKER_IMAGE_JENKINS" == "" ]]; then export export DOCKER_IMAGE_JENKINS='ros-ubuntu:16.04-pcl'; fi
   - if [[ "$ROS_DISTRO" == "melodic" && "$DOCKER_IMAGE_JENKINS" == "" ]]; then export export DOCKER_IMAGE_JENKINS='ros-ubuntu:18.04-pcl'; fi
 script:
+  # use https://github.com/ros-infrastructure/rosdep/pull/694 to respect version_lt for python pip, some package requries python3
+  - export BEFORE_SCRIPT="sudo apt-get install -y patchutils; curl -sL https://patch-diff.githubusercontent.com/raw/ros-infrastructure/rosdep/pull/694.diff | filterdiff --exclude='a/test/*' | sudo patch -d /usr/lib/python2.7/dist-packages/ -p2; $BEFORE_SCRIPT"
   - source .travis/travis.sh
   - (cd $TRAVIS_BUILD_DIR/doc && source setup.sh && make html)
 after_success: