circe failure to find implicit value for parameter d, with 0.2.0-SNAPSHOT

gistfile1.txt

CirceTest.scala
=================

package mvkpackage

import io.circe._
import cats.data.Xor
import scala.io.Source

object Main extends App {
  case class ServerConfig(
    val a: String = "test",
    val b: Int = 99
  )

  object ServerConfig2 {
    def derive[A](input: String): Xor[Error, A] =
      jawn.decode[A](input)

    implicit val ServerConfigDecoder: Decoder[ServerConfig] = Decoder.instance[ServerConfig]( c => {
      for {
        value <- (c.downField("a")).as[String] //c.as[ServerConfig]
      } yield ServerConfig(value)
    }
    )
  }

  val whatread = Source.fromFile("config.json").mkString
  val blah = ServerConfig2.derive[ServerConfig](whatread)
  println(blah)
}

config.json:
============
{"a":"dong","b":110}

build.sbt
==========
resolvers += "twitter-repo" at "http://maven.twttr.com"

resolvers += "Sonatype OSS Snapshots" at "https://oss.sonatype.org/content/repositories/snapshots"

//resolvers += Resolver.sonatypeRepo(“snapshots”)

scalaVersion := "2.11.6"

libraryDependencies ++= Seq(
    "io.circe" %% "circe-core" % "0.2.0-SNAPSHOT",
    "io.circe" %% "circe-generic" % "0.2.0-SNAPSHOT",
    "io.circe" %% "circe-jawn" % "0.2.0-SNAPSHOT"
)

Error:
=========
[error] /Users/mkelkar/tools/scala-circe/CirceTest.scala:16: could not find implicit value for parameter d: io.circe.Decoder[A]
[error]       jawn.decode[A](input)