Merge pull request #31 from scala-steward/update/sbt-sonatype-2.6

Update sbt-sonatype to 2.6

Author: TATSUNO Yasuhiro

project/plugins.sbt

@@ -1,6 +1,6 @@
 addSbtPlugin("org.scala-js"      % "sbt-scalajs"   % "0.6.28")
 addSbtPlugin("org.scalameta"     % "sbt-scalafmt"  % "2.0.4")
-addSbtPlugin("org.xerial.sbt"    % "sbt-sonatype"  % "2.5")
+addSbtPlugin("org.xerial.sbt"    % "sbt-sonatype"  % "2.6")
 addSbtPlugin("com.github.gseitz" % "sbt-release"   % "1.0.11")
 addSbtPlugin("com.jsuereth"      % "sbt-pgp"       % "1.1.2")
 addSbtPlugin("org.scoverage"     % "sbt-scoverage" % "1.6.0")