Fix configuration usage for sbt 0.13

src/main/scala-sbt-0.13/sbt/dependencygraph/DependencyGraphSbtCompat.scala

@@ -0,0 +1,7 @@
+package sbt.dependencygraph
+
+object DependencyGraphSbtCompat {
+  object Implicits {
+    implicit def convertConfig(config: sbt.Configuration): String = config.toString
+  }
+}

src/main/scala-sbt-1.0/sbt/dependencygraph/DependencyGraphSbtCompat.scala

@@ -0,0 +1,7 @@
+package sbt.dependencygraph
+
+object DependencyGraphSbtCompat {
+  object Implicits {
+    implicit def convertConfig(config: sbt.Configuration): sbt.Configuration = config
+  }
+}

src/main/scala/net/virtualvoid/sbt/graph/DependencyGraphSettings.scala

@@ -28,6 +28,8 @@ import net.virtualvoid.sbt.graph.util.IOUtil
 import internal.librarymanagement._
 import librarymanagement._
 
+import sbt.dependencygraph.DependencyGraphSbtCompat.Implicits._
+
 object DependencyGraphSettings {
   import DependencyGraphKeys._
   import ModuleGraphProtocol._