use the same httpclient to determine es version

[jipperinbham]

fixes #377

• CHANGELOG.md updated

[codecov]

Codecov Report

Merging #403 into master will decrease coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #403      +/-   ##
==========================================
- Coverage   84.27%   84.14%   -0.13%     
==========================================
  Files          61       61              
  Lines        4134     4138       +4     
==========================================
- Hits         3484     3482       -2     
- Misses        482      486       +4     
- Partials      168      170       +2

Impacted Files	Coverage Δ
adaptor/elasticsearch/elasticsearch.go	90.62% <100%> (+0.4%)	⬆️
adaptor/postgres/tailer.go	78.21% <0%> (-2.98%)	⬇️

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