Drop Scala 2.11 from Travis Java 8 and 9

Author: ashawley

Diff for: .travis.yml

@@ -35,6 +35,10 @@ matrix:
       env: SCALAJS_VERSION=1.0.0-M3
     - jdk: oraclejdk9
       env: SCALAJS_VERSION=1.0.0-M3
+    - scala: 2.11.12
+      jdk: oraclejdk8
+    - scala: 2.11.12
+      jdk: oraclejdk9
     - scala: 2.12.6
       jdk: openjdk6
     - scala: 2.13.0-M3