Update batch http link example in README

[matteodem]

To latest version with class called BatchHttpLink. Small change in the README file

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[codecov-io]

Codecov Report

Merging #504 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #504   +/-   ##
======================================
  Coverage    91.3%   91.3%           
======================================
  Files          19      19           
  Lines         828     828           
  Branches      204     204           
======================================
  Hits          756     756           
  Misses         67      67           
  Partials        5       5

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[evans]

Good catch! Thank you @matteodem