Fix codecov badge

[pgombar]

Description

Fix URL for codecov badge in README.

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PR information

• The title of the PR is clear and informative.
• There are a small number of commits, each of which has an informative message. This means that previously merged commits do not appear in the history of the PR. For information on cleaning up the commits in your pull request, see this page.
• Except for special cases involving multiple contributors, the PR is started from a fork of the main repository, not a branch.
• If applicable, the PR references the bug/issue that it fixes in the description.
• New Unit tests were added for the changes made and Travis.CI is passing.

Quality of Code and Contribution Guidelines

• I have read the contribution guidelines.

[codecov]

Codecov Report

Merging #1883 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #1883   +/-   ##
========================================
  Coverage    69.55%   69.55%           
========================================
  Files           83       83           
  Lines        11575    11575           
  Branches      1613     1613           
========================================
  Hits          8051     8051           
  Misses        3193     3193           
  Partials       331      331           

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