fix outdated rule name in README

make scalafix version consistenT

Author: taisukeoe

README.md

@@ -17,5 +17,6 @@ sbt ~tests/test
 1. Add sbt-scalafix: `addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.17")`
 2. Add SemanticDB: `addCompilerPlugin(scalafixSemanticdb)`
 3. Configure Semantic DB: `scalacOptions ++= List("-Yrangepos", "-P:semanticdb:synthetics:on")`
-4. Run the rule: `scalafix dependency:Scala213@org.scala-lang:scala-rewrites:0.1.0-SNAPSHOT`
-5. Run the rule on test sources: `Test/scalafix dependency:Scala213@org.scala-lang:scala-rewrites:0.1.0-SNAPSHOT`
+4. Run a rule you want: `scalafix dependency:RULE_NAME@org.scala-lang:scala-rewrites:0.1.0-SNAPSHOT`
+   For example, you can run Varargs rule by: `scalafix dependency:fix.scala213.Varargs@org.scala-lang:scala-rewrites:0.1.0-SNAPSHOT` 
+5. Run the rule on test sources: `Test/scalafix dependency:RULE_NAME@org.scala-lang:scala-rewrites:0.1.0-SNAPSHOT`

project/plugins.sbt

@@ -1 +1 @@
-addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.15")
+addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.17")