Add parameter for specify branch

Example with branch named 4.3.4
https://github.com/TrinityCore/TrinityCore/blob/4.3.4/README.md
Needs to be written as:

```
$.getGithubFileByFilePath("TrinityCore", "TrinityCore", "README.md?ref=4.3.4");
```

Btw. Thank you so much for this :)
:+1: 
