fix: potentially hangs on of WriteApi.Dispose()

[bednar]

Closes #79
Link to #68

• CHANGELOG.md updated
• Rebased/mergeable
• Tests pass
• Sign CLA (if not already signed)

[codecov-io]

Codecov Report

Merging #81 into master will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master      #81   +/-   ##
=======================================
  Coverage   15.96%   15.96%           
=======================================
  Files          47       47           
  Lines        4641     4641           
  Branches      224      224           
=======================================
  Hits          741      741           
  Misses       3880     3880           
  Partials       20       20           

Impacted Files	Coverage Δ
Client/WriteApi.cs	0.00% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update be35f47...939df04. Read the comment docs.