Update pekko version to 1.2.0 (#163)

Author: pjfanning

build.sbt

@@ -278,7 +278,7 @@ lazy val commonSettings =
 lazy val library =
   new {
     object Version {
-      val pekko         = "1.1.5"
+      val pekko         = "1.2.0"
       val pekkoHttp     = "1.2.0"
       val argonaut      = "6.3.11"
       val avro4s        = "4.1.2"