Update WipeTowerPrusaMM.cpp (#464)
Update WipeTowerPrusaMM.cpp (#464)

Resolves compile error on Win XP / Win 7 with native toolchain MinGW32-w64 on perl 5.26 or Citrusperl 5.24.
prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r