add [openjdk11] to Travis build matrix (rsocket#586)

Signed-off-by: Sean Sullivan <[email protected]>
Signed-off-by: Maksym Ostroverkhov <[email protected]>

Author: sullis

.travis.yml

@@ -18,7 +18,7 @@ language: java
 
 jdk:
 - oraclejdk8
-# - oraclejdk9
+- openjdk11
 
 env:
   global: