update scala doc

Author: wing328

docs/generators.md

@@ -57,7 +57,7 @@ The following generators are available:
 * [rust](generators/rust.md)  
 * [scala-akka](generators/scala-akka.md)  
 * [scala-gatling](generators/scala-gatling.md)  
-* [scala-sttp (beta)](generators/scala-sttp.md)  
+* [scala-sttp](generators/scala-sttp.md)  
 * [scalaz](generators/scalaz.md)  
 * [swift5](generators/swift5.md)  
 * [typescript (experimental)](generators/typescript.md)