Modefied cv_bridge to compile with Opencv4
ROS has pre-build debian package for cv_bridge. But it's incompatible to use OpenCV4 with some version of cv_bridge, which is build with OpenCV3.
In some cases, like using Jestson Xavier NX with Jetpack < 5.0, we can only use ros-melodic, while the official pre-install opencv (with cuda) is v4.1 (or higher). So I modefied the cv_bridge package to make it compatible with OpenCV4. Note that it's only work for ros-melodic, and I'll add supported version for ros-noetic if necessary in the future.
Add this repository to the same work space with other packages that you need to run. Then rebuild the whole workspace and your package will find the newer cv_bridge first.