Bump SBT and MiMa versions

Also note that we should bump sbt-osgi, which isn't quite
as simple as we need to deal with the AutoPlugin-ification
of that plugin.

After upgrading SBT, we can no longer append `Seq[File]` to
a `Seq[Credential]`. Not sure what changed, but I've been
more explicit rather than relying on the implicits.

Author: retronym

Diff for: build.sbt

@@ -29,6 +29,9 @@ repository in bintray          := "sbt-plugins"
 bintrayOrganization in bintray := None
 
 // this plugin depends on the sbt-osgi plugin -- 2-for-1!
+// TODO update to 0.8.0
+//      this might require us to modify the downstream project to enable the AutoPlugin
+//      See code changes and docs: https://github.com/sbt/sbt-osgi/commit/e3625e685b8d1784938ec66067d629251811a9d1
 addSbtPlugin("com.typesafe.sbt" % "sbt-osgi" % "0.7.0")
 
-addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "0.1.6")
+addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "0.1.8")

Diff for: project/build.properties

@@ -1 +1 @@
-sbt.version=0.13.1
+sbt.version=0.13.9

Diff for: src/main/scala/ScalaModulePlugin.scala

@@ -60,7 +60,7 @@ object ScalaModulePlugin extends Plugin {
     ),
     credentials ++= {
       val file = Path.userHome / ".ivy2" / ".credentials"
-      if (file.exists) List(file) else Nil
+      if (file.exists) List(new FileCredentials(file)) else Nil
     },
 
     publishMavenStyle    := true,