[MJAR-280] Java 8 minimum (#29)

* [MJAR-280] Java 8 minimum
* bump version to 3.3.0

Signed-off-by: Olivier Lamy <olamy@apache.org>

pom.xml

@@ -30,7 +30,7 @@
   </parent>
 
   <artifactId>maven-jar-plugin</artifactId>
-  <version>3.2.3-SNAPSHOT</version>
+  <version>3.3.0-SNAPSHOT</version>
   <packaging>maven-plugin</packaging>
 
   <name>Apache Maven JAR Plugin</name>
@@ -81,7 +81,7 @@
     <!-- TODO remove with Maven APi upgrade -->
     <!-- the same version as in Maven 3.1.0 -->
     <sisuVersion>0.0.0.M2a</sisuVersion>
-    <javaVersion>7</javaVersion>
+    <javaVersion>8</javaVersion>
     <project.build.outputTimestamp>2022-01-08T21:19:21Z</project.build.outputTimestamp>
   </properties>