lume.format(str, table) doesn't properly handle false values

Simple test:

```lua
local t = lume.format("{1} is {2} is {3}", { true, false, true })
print(t) -- true is {2} is true

```

I guess this is of the way Lua deals with false values, not sure what a proper fix would be, but if I can figure one out I will send a PR.