Syntax highlight bug: `'`()

The following code gets highlighted incorrectly:

```scala
def `'`() = ()
`'`()
```

[Demo](https://github-lightshow.herokuapp.com/?utf8=%E2%9C%93&scope=from-url&grammar_url=https%3A%2F%2Fgithub.com%2Fatom-community%2Flanguage-scala%2Fblob%2Fv1.1.9%2Fgrammars%2Fscala.cson&grammar_text=&code_source=from-url&code_url=https%3A%2F%2Fgist.githubusercontent.com%2Fmkantor%2F127b02ac08b37e42ca84610b34cfb824%2Fraw%2F8f3172896fbafd31db7f81249e4bed9aaec2aeb4%2FBacktickSingleQuote.scala&code=).

This exact same bug is present in the Scala TextMate bundle (mads-hartmann/scala.tmbundle/issues/59), which is currently used by [Linguist](https://github.com/github/linguist), so you'll see the same problem in the code block above.

Start with grammars/scala.cson from the linked language package and reproduce the highlighting for the provided `def `'`() = ()` and ``'`()`` snippet. Compare the behavior with the linked Scala TextMate bundle issue and verify that the corrected grammar highlights both declarations and calls consistently.

Written by the indexing model from the issue text.