Parent is not relatively reachable for this project (#231)

Fixes warning:
[WARNING] 'parent.relativePath' of POM jakarta.json:jakarta.json-api:2.0.0-SNAPSHOT (.../jsonp/api/pom.xml) points at org.glassfish:json instead of org.eclipse.ee4j:project, please verify your project structure @ line 23, column 13
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.

Signed-off-by: Piotrek Zygielo <piotr@zygielo.pl>
diff --git a/api/pom.xml b/api/pom.xml
index 79ef1a3..c71f578 100644
--- a/api/pom.xml
+++ b/api/pom.xml
@@ -24,6 +24,7 @@
         <groupId>org.eclipse.ee4j</groupId>
         <artifactId>project</artifactId>
         <version>1.0.6</version>
+        <relativePath/>
     </parent>
 
     <groupId>jakarta.json</groupId>