Align Java source code level to Gerrit 1.7

Change-Id: I0f59021f2875c28414fa5826176272d02e733522

pom.xml

diff --git a/pom.xml b/pom.xml
index f94f05b..79018a6 100644
--- a/pom.xml
+++ b/pom.xml
@@ -96,8 +96,8 @@
         <artifactId>maven-compiler-plugin</artifactId>
         <version>2.5.1</version>
         <configuration>
-          <source>1.6</source>
-          <target>1.6</target>
+          <source>1.7</source>
+          <target>1.7</target>
         </configuration>
       </plugin>
       <plugin>