Update .travis.yml (#149)

* Update .travis.yml

Update to use JDKs that are available:
https://docs.travis-ci.com/user/reference/trusty/#JVM-(Clojure%2C-Groovy%2C-Java%2C-Scala)-images

* Update pom.xml

Update javadoc plugin version

Author: stolstov

.travis.yml

@@ -1,7 +1,8 @@
 language: java
 jdk:
-    - openjdk6
     - openjdk7
-    - oraclejdk7
+    - openjdk8
+    - oraclejdk8
+    - oraclejdk9
 notifications:
-    email: false
+    email: false

pom.xml

@@ -104,7 +104,7 @@
 		<!-- plugin versions -->
 		<compiler.plugin.version>2.3.1</compiler.plugin.version>
 		<source.plugin.version>2.2.1</source.plugin.version>
-		<javadoc.plugin.version>2.9</javadoc.plugin.version>
+		<javadoc.plugin.version>3.0.0-M1</javadoc.plugin.version>
 	</properties>
 
 	<dependencies>