Install luabitop from src rock on travis
Install luabitop from src rock on travis

Fixes Travis failure when attempting to fetch luabitop sources
from luajit.org, which has blocked downloads from travis recently.

keplerproject/luarocks,starius/luarocks,luarocks/luarocks,starius/luarocks,tarantool/luarocks,robooo/luarocks,xpol/luavm,xpol/luarocks,tarantool/luarocks,xpol/luavm,xpol/luarocks,xpol/luavm,ignacio/luarocks,xpol/luavm,ignacio/luarocks,xpol/luarocks,xpol/luainstaller,xpol/luainstaller,keplerproject/luarocks,starius/luarocks,tarantool/luarocks,xpol/luainstaller,luarocks/luarocks,ignacio/luarocks,robooo/luarocks,robooo/luarocks,robooo/luarocks,xpol/luavm,xpol/luainstaller,xpol/luarocks,ignacio/luarocks,luarocks/luarocks,starius/luarocks,keplerproject/luarocks,keplerproject/luarocks