fix: Close the response body of a WriteBatch call

[maxmora]

Proposed Changes

Closes the response body after making a WriteBatch call. Failing to close the response body was keeping OpenCensus spans from being exported when using ochttp.Transport (see: https://github.com/census-instrumentation/opencensus-go/blob/49838f207d61097fc0ebb8aeef306913388376ca/plugin/ochttp/trace.go#L94)

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• Tests pass
• Commit messages are in semantic format
• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Merging #300 (63bcf73) into master (ada9e3b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #300   +/-   ##
=======================================
  Coverage   91.84%   91.84%           
=======================================
  Files          23       23           
  Lines        2036     2036           
=======================================
  Hits         1870     1870           
  Misses        111      111           
  Partials       55       55           

---

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 ada9e3b...63bcf73. Read the comment docs.

[vlastahajek]

Thanks for the fix and PR!