Correct 'git submodule' syntax (#5654)
Correct 'git submodule' syntax (#5654)

Should be singular, not plural (submodule, not submodules)
Lan-Hekary/Arduino,esp8266/Arduino,Lan-Hekary/Arduino,sticilface/Arduino,sticilface/Arduino,esp8266/Arduino,esp8266/Arduino,sticilface/Arduino,esp8266/Arduino,Lan-Hekary/Arduino,sticilface/Arduino,sticilface/Arduino,Lan-Hekary/Arduino,esp8266/Arduino,Lan-Hekary/Arduino