Issue title: Cannot display Chinese characters in Mac OS
 Issue body: I use this package with the "love" example and find that the results are both OK in Win10 and Ubuntu 16.04, however when I run the code in Mac OS, the Chinese characters cannot display correctly, they only show polygons. I also use wordcloud package and find the Chinese characters are OK, too. Even I set the text family in theme function, it doesn't work.
 Comments: 
 Comment 0: Thank you for your feedback. I'm aware of this kind of issue. Font handling
is something very tricky and I don't have OS X. Do you have the same issue
using the original geom_text ?

On Wed, Oct 23, 2019 at 2:51 AM tiger <shawn02@example.com> wrote:

> I use this package with the "love" example and find that the results are
> both OK in Win10 and Ubuntu 16.04, however when I run the code in Mac OS,
> the Chinese characters cannot display correctly, they only show polygons. I
> also use wordcloud package and find the Chinese characters are OK, too.
> Even I set the text family in theme function, it doesn't work.
>
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 Comment 1: Yes, they are the same problem. I use the same method to modify the code, the Chinese character can display correctly while other language characters become polygons with the following code.
```
set.seed(42)
ggplot(love_words_small, aes(label = word)) +
    geom_text_wordcloud(family = "Kai") +
    theme_minimal()
```
So, for multiple languages, which font family should be chosen to this problem?
 Comment 2: If I get it correctly, you should either find a font that includes both
latin and chinese characters or use a different font for the two different
cases...

On Thu, Oct 24, 2019 at 2:59 PM tiger <shawn02@example.com> wrote:

> Yes, they are the same problem. I use the same method to modify the code,
> the Chinese character can display correctly while other language characters
> become polygons with the following code.
>
> set.seed(42)
> ggplot(love_words_small, aes(label = word)) +
>     geom_text_wordcloud(family = "Kai") +
>     theme_minimal()
>
> So, for multiple languages, which font family should be chosen to this
> problem?
>
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{'source': 'GithubIssues', 'repo_name_with_owner': 'lepennec/ggwordcloud', 'issue_id': 511007401, 'repo_stars': 154.0}