Make extra space after emoji optional

I am running the latest HEAD for NeoVim + the latest nightly of iTerm2, both of these things together allow for correct rendering of emoji with no character width problems or background color issues.

This means that the extra space which this plugin inserts after emoji is no longer required for my setup:
```diff
function! s:emoji(name, ...)
if b:github_emoji && has_key(s:emoji_code, tolower(a:name))
let e = s:emoji_code[tolower(a:name)]
- return join(map(copy(e), 'nr2char(v:val)'), '') . repeat(' ', 1 + (a:0 > 0 ? a:1 : 0))
+ return join(map(copy(e), 'nr2char(v:val)'), '') . repeat(' ', (a:0 > 0 ? a:1 : 0))
else
return ''
endif
endfunction
```

Would it be possible to make this an option that can be set via `g:github_dashboard`?