Makefile: fix parameter -e printed by echo
Makefile: fix parameter -e printed by echo

It seems that on linux only inside a makefile the parameter after the echo
command gets printed if no single quoted sting comes afterwards so I had
to switch to single quotes such that I can use the parameter.

PX4/Firmware,mcgill-robotics/Firmware,mcgill-robotics/Firmware,acfloria/Firmware,dagar/Firmware,PX4/Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,acfloria/Firmware,PX4/Firmware,mcgill-robotics/Firmware,Aerotenna/Firmware,acfloria/Firmware,Aerotenna/Firmware,acfloria/Firmware,PX4/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,dagar/Firmware,mcgill-robotics/Firmware,PX4/Firmware,mcgill-robotics/Firmware,mcgill-robotics/Firmware,dagar/Firmware,krbeverx/Firmware,krbeverx/Firmware,dagar/Firmware,Aerotenna/Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,Aerotenna/Firmware,dagar/Firmware,dagar/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,dagar/Firmware,krbeverx/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware