pom: update to nfs4j-0.7.7

Changelog for nfs4j-0.7.6..nfs4j-0.7.7
    * [94db02f] calculate index in the FsExport constructor

Target: 2.8, 2.7, 2.6
Require-book: no
Require-notes: no
Merge pull request #968 from kofemann/update-nfs-2.7

pom: update to nfs4j-0.7.7