Handle multiple possible emoji in a row

Currently, if there are two possible emoji in a row, the first one is stripped:

``` ruby
io = StringIO.new("i like #hashtags and 1direction they are the #1 band")
Rumoji.encode_io(io).string
# actual:   => "i like #hashtags and 1direction they are the 1 band"
# expected: => "i like #hashtags and 1direction they are the #1 band"
```

This branch fixes it.