(chore) Add Java 9 build to travis matrix.

The Java 9 build is allowed to fail for now. It should be able to
possibly work once gradle/gradle#890 is
fixed.

.travis.yml

@@ -7,6 +7,7 @@ addons:
     packages:
       - gdb
       - oracle-java8-installer
+      - oracle-java9-installer
 
 # keep gradle cache.
 before_cache:
@@ -30,6 +31,12 @@ matrix:
       env:
         - USE_FRAMEBUFFER=false
         - _JAVA_OPTIONS="-Djava.awt.headless=true -Dtestfx.robot=glass -Dtestfx.headless=true -Dprism.order=sw -Dprism.text=t2k -Dtestfx.setup.timeout=2500"
+    - os: linux
+      dist: trusty
+      jdk: oraclejdk9
+      env:
+        - USE_FRAMEBUFFER=true
+        - _JAVA_OPTIONS="--add-exports=javafx.graphics/com.sun.glass.ui=ALL-UNNAMED"
     - os: osx
       osx_image: xcode8.2
       env:
@@ -45,6 +52,10 @@ matrix:
     - env:
       - OSX_HEADLESS=false
       - _JAVA_OPTIONS="-Dprism.order=sw"
+    - env:
+      - USE_FRAMEBUFFER=true
+      - _JAVA_OPTIONS="--add-exports=javafx.graphics/com.sun.glass.ui=ALL-UNNAMED"
+
 
 before_script:
   - echo $HOME