Revert "Update sbt-mima-plugin to 0.3.0"

This reverts commit 881dbe4.

Author: SethTisue

build.sbt

@@ -28,4 +28,5 @@ bintrayOrganization := None
 // We still run our plugin builds for 2.11 on Java 6, so we cannot upgrade.
 addSbtPlugin("com.typesafe.sbt" % "sbt-osgi" % "0.8.0")
 
-addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "0.3.0")
+// can't be upgraded to 0.3.0 which requires Java 8
+addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "0.1.18")