Rename the project umbrella setting to akka

See #4 (comment)
The usage of `projectName` is there: https://github.com/knutwalker/sbt-knutwalker/blob/42918db01aa9b55dce94d82d53ff2eef94a43860/src/main/scala/de/knutwalker/sbt/KSbtPlugin.scala#L167

project/Build.scala

@@ -30,7 +30,7 @@ object Build extends AutoPlugin {
 
   override lazy val projectSettings = Seq(
            git.baseVersion := "3.0.0",
-               projectName := "akka-stream-json",
+               projectName := "akka", // see https://github.com/knutwalker/akka-stream-json/pull/4#issuecomment-244199557 for why it's akka and not akka-stream-json
               organization := "de.knutwalker",
                description := "Json support for Akka Streams/Http via Jawn",
                 maintainer := "Paul Horn",