Lenv is failing to download LuaJIT

[atstep01]

Recently my docker builds started failing while installing lenv. Seems that the link to download luajit is broken

download http://luajit.org/download.html
+ /usr/bin/curl -L --compressed http://luajit.org/download.html
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0curl: (7) Failed to connect to luajit.org port 80: Connection refused
No such file or directory at /root/.lenv/bin/lenv line 79.
The command '/bin/sh -c . ~/.lenvrc    && lenv fetch    && lenv install 5.3.4    && lenv use 5.3.4' returned a non-zero code: 2

[cbeeler]

I think https://github.com/mah0x211/lenv/blob/master/lenv#L585 needs updating to https://. Let me get some testing in before I make a PR.