Bump assertj-core from 1.7.1 to 2.9.1

diff --git a/pom.xml b/pom.xml
index 6935051..080b5e8 100644
--- a/pom.xml
+++ b/pom.xml
@@ -164,7 +164,7 @@
       <dependency>
         <groupId>org.assertj</groupId>
         <artifactId>assertj-core</artifactId>
-        <version>1.7.1</version>
+        <version>2.9.1</version><!-- Java 7 -->
       </dependency>
     </dependencies>
   </dependencyManagement>