mingw cross-compilation fails when looking for Windows.h

[nbarrios1337]

https://github.com/vincentlaucsb/csv-parser/blob/9d5f796a32c6cdecd83a2f778ca6db0500948d27/include/internal/common.hpp#L16

Due to the capitalization of the includes directive, MinGW errors out when cross-compiling on Linux targeting Windows. Fortunately this is the only instance this problem, as all other instances of #include <windows.h> in csv-parser are lowercase.