(Puppetfile) bump derdanne/nfs to include dep patches

See: voxpupuli/puppet-nfs#170

Puppetfile

@@ -4,7 +4,7 @@ mod 'camptocamp/augeas', '1.9.0'
 mod 'ccin2p3/etc_services', '2.0.3'
 mod 'ccin2p3/mit_krb5', git: 'https://github.com/lsst-it/puppet-mit_krb5.git', branch: 'f8f0242'  # https://github.com/ccin2p3/puppet-mit_krb5/pull/29 https://github.com/ccin2p3/puppet-mit_krb5/pull/34 https://github.com/ccin2p3/puppet-mit_krb5/pull/35
 mod 'cirrax/libvirt', '5.0.1'
-mod 'derdanne/nfs', '2.1.8'
+mod 'derdanne/nfs', git: 'https://github.com/lsst-it/puppet-nfs', ref: '6d51f51'  # https://github.com/derdanne/puppet-nfs/pull/170
 mod 'duritong/sysctl', git: 'https://github.com/duritong/puppet-sysctl', ref: '847ec1c'  # migrate to herculesteam/augeasproviders_sysctl; https://github.com/duritong/puppet-sysctl/pull/48
 mod 'example42/network', git: 'https://github.com/lsst-it/puppet-network', ref: 'v3.6.1'  # unmaintained. Migrate to puppet/network?
 mod 'fervid/snapd', '1.2.1' # 2021-05-31 hreinking: snapd for EAS Raspberry Pi