all: add 'oraclejdk10' to travis build matrix

diff --git a/.travis.yml b/.travis.yml
index 9ed0023..ada69d9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -45,6 +45,7 @@
 jdk:
   - oraclejdk8
   - oraclejdk9
+  - oraclejdk10
 
 notifications:
   email: false