no more Gitter room

references scala#222

Author: SethTisue

README.md

@@ -76,4 +76,4 @@ details.
 
  * See the [Scala Developer Guidelines](https://github.com/scala/scala/blob/2.13.x/CONTRIBUTING.md) for general contributing guidelines
  * Have a look at [existing issues](https://github.com/scala/scala-parser-combinators/issues)
- * Ask questions and discuss [on Gitter](https://gitter.im/scala/scala-parser-combinators)
+ * Feel free to open draft pull requests with partially completed changes, to get feedback.