Use lua from github mirror on posix as well #796

Job	Run time
Mac-os-aarch64	1m 5s
Mac-os	2m 13s
Android (21.4.7075529)	2m 28s
Linux-musl (travis-core-linux-musl)	1m 46s
Android (16.1.4479499)	3m 0s
Linux-musl (travis-core-linux-musl-apicheck)	1m 44s
Android (26.1.10909125)	1m 52s
Mac-os-aarch64-cctools	2m 36s
Linux-musl (travis-core-linux-musl-aarch64)	1m 52s
Mac-os-cctools	2m 35s
Windows-visual-studio (Win32)	1m 29s
Windows-mingw (win32)	1m 39s
Windows-visual-studio (x64)	1m 59s
Windows-mingw (x64)	1m 25s
Mac-os-universal	14s
Mac-os-universal-cctools	6s
Notify-success	2s
	28m 5s

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