try building with JDK9 on travis (will revert Publisher change)

Author: ktoso

.java-version

@@ -0,0 +1 @@
+9-ea

.travis.yml

@@ -1,5 +1,12 @@
 language: java
 sudo: required
+before_install:
+  - sudo apt-get update -qq
+  - sudo apt-get install oracle-9-installer
+  - remove_dir_from_path $JAVA_HOME/bin
+  - export JAVA_HOME=/usr/lib/jvm/java-9-oracle
+  - export PATH=$JAVA_HOME/bin:$PATH
+  - java -version
 script:
   - ./gradlew check
 cache:
@@ -8,6 +15,7 @@ cache:
 jdk:
   - oraclejdk8
   - openjdk6
+  - oraclejdk9
 env:
   global:
   - TERM=dumb

api/src/main/java/org/reactivestreams/Publisher.java

@@ -11,6 +11,10 @@
 
 package org.reactivestreams;
 
+// FIXME THIS IS ONLY TO CHECK THAT JDK9 BUILD WORKED ON TRAVIS
+import java.util.concurrent.Flow; // REMOVE THIS
+// FIXME THIS IS ONLY TO CHECK THAT JDK9 BUILD WORKED ON TRAVIS
+
 /**
  * A {@link Publisher} is a provider of a potentially unbounded number of sequenced elements, publishing them according to
  * the demand received from its {@link Subscriber}(s).