🐛 📚 [CppCon-2018] GUnit lightning talk - typo fix

Problem:
- There is a horizontal line instead of new slide.

Solution:
- Add additional '-' to create new slide instead of a horizontal line.

Author: kris-jusiak

docs/cppcon-2018/index.html

@@ -47,7 +47,7 @@
 
 #### [kris@jusiak.net](mailto:kris@jusiak.net) | [@krisjusiak](https://twitter.com/krisjusiak) | [linkedin.com/in/kris-jusiak](https://www.linkedin.com/in/kris-jusiak)
 
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 ### Testing