Update libpng to 1.6.37

[mrodozov]

Update libpng for what tensorflow 2.1 uses now
https://github.com/tensorflow/tensorflow/blob/r2.1/tensorflow/workspace.bzl#L271

[mrodozov]

please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-run-pr-tests/4434/console Started: 2020/01/30 16:44

[cmsbuild]

A new Pull Request was created by @mrodozov (Mircho Rodozov) for branch IB/CMSSW_11_1_X/master.

@cmsbuild, @smuzaffar, @mrodozov, @tulamor can you please review it and eventually sign? Thanks.
cms-bot commands are listed here

[cmsbuild]

+1
Tested at: 3b0c25f
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-07719a/4434/summary.html
CMSSW: CMSSW_11_1_X_2020-01-30-1100
SCRAM_ARCH: slc7_amd64_gcc820

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-07719a/4434/summary.html

Comparison Summary:

• No significant changes to the logs found
• Reco comparison results: 0 differences found in the comparisons
• DQMHistoTests: Total files compared: 34
• DQMHistoTests: Total histograms compared: 2697068
• DQMHistoTests: Total failures: 1
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 2696721
• DQMHistoTests: Total skipped: 346
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 33 files compared)
• Checked 147 log files, 16 edm output root files, 34 DQM output files

[mrodozov]

+externals
it's described above why we need this update

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next IB/CMSSW_11_1_X/master IBs (tests are also fine). This pull request will now be reviewed by the release team before it's merged. @davidlange6, @silviodonato, @fabiocos (and backports should be raised in the release meeting by the corresponding L2)