Upgrade to assertj 2.0.0

Changelog:

http://joel-costigliola.github.io/assertj/assertj-core-news.html#assertj-core-2.0.0

pom.xml

@@ -299,7 +299,7 @@
       <groupId>org.assertj</groupId>
       <artifactId>assertj-core</artifactId>
       <scope>test</scope>
-      <version>1.7.1</version>
+      <version>2.0.0</version>
     </dependency>
     <dependency>
       <groupId>org.eclipse.jetty</groupId>