`\^downarrow` and `\^uparrow` don't tab complete

`julia-vim` does not appear to tab complete `\^downarrow` to the unicode character `ꜜ`, and same for `\^uparrow` to `ꜛ`. Both work in the REPL for me. This would be nice to have since `\downarrow` and `\uparrow` can't be used in Julia identifiers, so those are nice alternatives.