variables with `false` values are not accessible

[Aliaksandr Rahalevich]

$ cat /tmp/1.lua

local up = false

local f = function()
    local x = false
    local y = true
    require('resty.repl').start()
end

f()

$ lua /tmp/1.lua 
[1] lua(main)> x
=> nil
[2] lua(main)> y
=> true
[3] lua(main)> up
=> nil