Revert "Only target JDK 8 in tests, restore JDK 7 as minimum required version"

This reverts commit 60c9116.

Reason for revert: some dependencies already require JDK 8 anyway

Author: tbroyer

pom.xml

@@ -65,7 +65,7 @@
 
   <properties>
     <mavenVersion>3.3.1</mavenVersion>
-    <targetJdk>7</targetJdk>
+    <targetJdk>8</targetJdk>
 
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <project.build.outputEncoding>UTF-8</project.build.outputEncoding>