Fix include path for ./parsers

[yh-sb]

libnmea build error was added by https://github.com/jacketizer/libnmea/pull/46 😔

Since src/parsers directory wasn't in include path, it leads to the following error while compiling libnmea:

src/parsers/gpgga.h:7:10: fatal error: nmea.h: No such file or directory
    7 | #include <nmea.h>