Run travis build against Oracle jdks 8 and 9

Author: rowanseymour

.travis.yml

@@ -2,3 +2,4 @@ language: java
 install: mvn install -DskipTests=true -Dgpg.skip=true
 jdk:
   - oraclejdk8
+  - oraclejdk9

pom.xml

@@ -107,7 +107,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
-                <version>3.3</version>
+                <version>3.7.0</version>
                 <!-- compile for Java 1.7 -->
                 <configuration>
                     <source>1.7</source>
@@ -118,7 +118,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-source-plugin</artifactId>
-                <version>2.4</version>
+                <version>3.0.1</version>
                 <executions>
                     <execution>
                         <id>attach-sources</id>
@@ -131,7 +131,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-javadoc-plugin</artifactId>
-                <version>2.10.3</version>
+                <version>3.0.0-M1</version>
                 <executions>
                     <execution>
                         <id>attach-javadocs</id>
@@ -162,7 +162,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-release-plugin</artifactId>
-                <version>2.5.2</version>
+                <version>2.5.3</version>
                 <executions>
                     <execution>
                         <id>default</id>
@@ -183,7 +183,7 @@
             <plugin>
                 <groupId>org.sonatype.plugins</groupId>
                 <artifactId>nexus-staging-maven-plugin</artifactId>
-                <version>1.6.6</version>
+                <version>1.6.8</version>
                 <extensions>true</extensions>
                 <configuration>
                     <serverId>ossrh</serverId>