編譯Cartographer 的過程中，出現了無法下載ceres-solver的問題
Failed to clone repository:
'https://ceres-solver.googlesource.com/ceres-solver'
修改對應的CMakeLists.txt文件， 比如我的是
/home/sean/catkin_ws/src/cartographer_ros/ceres_solver/CMakeLists.txt
將其中的https://ceres-solver.googlesource.com/ceres-solver 改爲
https://github.com/ceres-solver/ceres-solver.git
就可以了
如果編譯cartographer_ros的話
1》 修改catkin_ws/src/.rosinstall 文件
2》 修改catkin_ws/src/cartographter_ros/cartographter_ros.rosinstall 文件
將兩個文件中的ceres-solver路徑改爲github下的倉庫