Merge pull request #411 from scala-steward/update/http4s-blaze-server-0.21.0-RC4

Update http4s-blaze-server, http4s-dsl to 0.21.0-RC4

Author: mergify[bot]

project/Versions.scala

@@ -1,5 +1,5 @@
 object Versions {
-  val http4s = "0.21.0-RC3"
+  val http4s = "0.21.0-RC4"
   val catsEffect = "2.1.0"
   val circe = "0.12.3"
   val circeYaml = "0.12.0"