Update pom.xml

updated sling.java.version to 8
diff --git a/pom.xml b/pom.xml
index f00e6f8..80db165 100644
--- a/pom.xml
+++ b/pom.xml
@@ -54,7 +54,7 @@
               - 8: Java 8
               - 9: Java 9
         -->
-        <sling.java.version>7</sling.java.version>
+        <sling.java.version>8</sling.java.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <surefire.plugin.version>2.20.1</surefire.plugin.version>