configure.ac: fix regeneration of luaposix.rockspec
configure.ac: fix regeneration of luaposix.rockspec

rrthomas/luaposix,ardje/luaposix,zevv/luaposix,jimmyharris/luaposix,luaposix/luaposix,snegovick/luaposix,rrthomas/luaposix,snegovick/luaposix,jimmyharris/luaposix,ardje/luaposix,zevv/luaposix