Update sbt-mima-plugin to 1.2.1 (#675)

Author: scala-steward

project/plugins.sbt

@@ -8,7 +8,7 @@ addSbtPlugin("com.github.sbt" % "sbt-release" % "1.5.0")
 addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.3.2")
 addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.4.8")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.4.4")
-addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "1.2.0")
+addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "1.2.1")
 addSbtPlugin("org.scoverage" % "sbt-coveralls" % "1.3.15")
 addSbtPlugin("com.github.sbt" % "sbt-git" % "2.2.0")
 addSbtPlugin("com.eed3si9n" % "sbt-salad-days" % "0.2.0")