Fix release docs

Author: nicolasstucki

docs/blog/_posts/2020-03-18-23rd-dotty-milestone-release.md

@@ -221,7 +221,7 @@ Macro.scala
 import scala.quoted._
 
 inline def showTree(inline x: Any): String = ${ showTreeImpl('x) }
-def showTreeImpl(x: Expr[Any])(using qctx: Quotes): Expr[String] =
+def showTreeImpl(x: Expr[Any])(using qctx: QuoteContext): Expr[String] =
   import qctx.tasty._
   x.unseal match
     case Inlined(_, _, app: Apply) =>