libs: update nfs library

bugfix version:

Changelog for nfs4j-0.6.2..nfs4j-0.6.3
    * [ebf7974] nfsv3: fix hard link creation (similar to http://rb.dcache.org/r/6224)

Acked-by: Paul Millar
Target: master, 2.7, 2.6
Require-book: no
Require-notes: no

pom.xml

@@ -777,7 +777,7 @@
         <dependency>
             <groupId>org.dcache</groupId>
             <artifactId>nfs4j-core</artifactId>
-            <version>0.6.2</version>
+            <version>0.6.3</version>
             <exclusions>
                 <exclusion>
                     <groupId>org.dcache.chimera</groupId>