Add tag to rockspec #65

Job	Run time
windows (lua53, lua5.3, 5.3, /mingw64/include/lua5.3/)	3m 37s
unix (5.1, ubuntu-latest)	41s
windows (lua, lua, 5.4, /mingw64/include/)	3m 23s
windows (luajit, luajit, 5.1, /mingw64/include/luajit-2.1/)	3m 15s
unix (5.1, macos-latest)	1m 43s
unix (5.2, ubuntu-latest)	47s
unix (5.2, macos-latest)	2m 17s
unix (5.3, ubuntu-latest)	39s
unix (5.3, macos-latest)	1m 42s
unix (5.4, ubuntu-latest)	41s
unix (5.4, macos-latest)	1m 44s
unix (luajit-2.1.0-beta3, ubuntu-latest)	37s
unix (luajit-2.1.0-beta3, macos-latest)	2m 12s
unix (luajit-openresty, ubuntu-latest)	33s
unix (luajit-openresty, macos-latest)	1m 38s
	25m 29s

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