‘runtime_error’ is not a member of ‘std’

[C-H-Chien]

Hi,

An error was met during the compilation:
Structure-PLP-SLAM/src/pangolin_viewer/color_scheme.cc:45:24: error: ‘runtime_error’ is not a member of ‘std’`

std::runtime_error is defined in the header <stdexcept> (according to this), so placing #include <stdexcept> in src/pangolin_viewer/color_scheme.h could solve the issue.