Warning in toRoman()

[RobTillaart]

printHelpers.cpp: In function 'char* toRoman(uint32_t)':
printHelpers.cpp:458:23: warning: comparison between signed and unsigned integer
expressions [-Wsign-compare]

     for (int i = 0; i < strlen(buffer); i++)
                     ~~^~~~~~~~~~~~~~~~

Low prio but should be fixed.