add OpenJDK 11 to CI matrix

Author: SethTisue

.travis.yml

@@ -6,6 +6,7 @@ scala:
   - 2.13.0-M5
 jdk:
   - oraclejdk8
+  - openjdk11
 env:
   global:
 

project/plugins.sbt

@@ -1,7 +1,7 @@
 if (System.getProperty("java.version").startsWith("1."))
   Seq()
 else
-  // override to version that works on Java 9,
+  // override to version that works on Java 11,
   // see https://github.com/scala/sbt-scala-module/issues/35
   Seq(addSbtPlugin("com.typesafe.sbt" % "sbt-osgi" % "0.9.3"))