Work around dependency conflict in latest DNSClient

[gwynne]

Pins DNSClient to a version that doesn't exhibit the conflict for now.

[codecov-commenter]

Codecov Report

Merging #59 (bbafd45) into main (6129661) will not change coverage. The diff coverage is n/a.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #59 +/- ## ======================================= Coverage 72.59% 72.59% ======================================= Files 20 20 Lines 686 686 ======================================= Hits 498 498 Misses 188 188 ```

[VaporBot]

These changes are now available in 1.3.1