Fix broken links to "Package Sealing" in the JAR spec

To reproduce, open http://download.java.net/java/jdk9/docs//specs/jar/jar.html and click on 'versioning' link in "attributes defined for package versioning and sealing information" sentence.
http://download.java.net/java/jdk9/docs//specs/versioning/index.html -> Not Found

There are also a couple broken links to "The JAR File Specification: Package Sealing" in java.lang and java.util.jar.