Show line numbers in vim based on terminal size

.vimrc

" I like having line numbers on, but don't want to wrap lines in a
" standard-sized terminal window.
fun! WinSizeAutoNumber()
    if winwidth(0) > 84
        set number
    else
        set nonumber
    endif
endfunction

" Run once on startup
call WinSizeAutoNumber()

" Run when window is resized
au VimResized * call WinSizeAutoNumber()