Update Mockito and add CI for JDK9/10/11 (#87)

* Add travis for openjdk9,10,11

* Update mockito to 2.23.0

This updates mockito, for the sake of getting tests to work on JDK10 and JDK11.

Author: johnwalker

.travis.yml

@@ -1,8 +1,10 @@
 language: java
 jdk:
   - openjdk8
+  - openjdk9
+  - openjdk10
+  - openjdk11
   - oraclejdk8
-#  - openjdk9 # Not yet supported by travis
   - oraclejdk9
 script: mvn install -Dgpg.skip=true
 sudo: false

pom.xml

@@ -55,7 +55,7 @@
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-core</artifactId>
-            <version>2.8.47</version>
+            <version>2.23.0</version>
             <scope>test</scope>
         </dependency>