Update dependency hpcloud/tail to the successor nxadm/tail

[thomas-kaltenbach]

• A short explanation of the proposed change:
  Update dependency hpcloud/tail to the successor nxadm/tail (fork). hpcloud/tail is not longer maintained.

• An explanation of the use cases your change solves
  We currently face some issues on our live landscapes. We see that many logs are missing after the logrotation (see issue The logs forwarding by syslog got lost syslog-release#64).
  @b1tamara and I debugged the problem and we are sure that something goes wrong in the hpcloud/tail library.
  We saw that hpcloud/tail is not longer maintained and the successor is nxadm/tail. Many issues are solved in the meantime in this fork. We hope that this will maybe also solve our problems.

• Instructions to functionally test the behavior change using operator interfaces (BOSH manifest, logs, curl, and metrics)
  Logs should be still forwarded.

• Expected result after the change
  Fix issues with logrotation i.e. Overview of reviewed/fixed/applied issues/PRs of the abandoned upstream (fixed on nxadm/tail) nxadm/tail#6

• I have viewed signed and have submitted the Contributor License Agreement

• I have made this pull request to the master branch

• I have run all the unit tests using scripts/test from blackbox.