Changed codecov to run on py3.8

[larohra]

Description

Fix travis to run codecoverage on 3.8 instead of 3.7

Issue #

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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 #1875 into develop will increase coverage by 0.25%.
The diff coverage is 28.78%.

@@             Coverage Diff             @@
##           develop    #1875      +/-   ##
===========================================
+ Coverage    69.45%   69.71%   +0.25%     
===========================================
  Files           82       82              
  Lines        11469    11593     +124     
  Branches      1619     1625       +6     
===========================================
+ Hits          7966     8082     +116     
- Misses        3166     3172       +6     
- Partials       337      339       +2     

Impacted Files	Coverage Δ
azurelinuxagent/common/osutil/freebsd.py	44.06% <0.00%> (+1.38%)	⬆️
azurelinuxagent/common/osutil/nsbsd.py	41.66% <0.00%> (+0.96%)	⬆️
azurelinuxagent/common/osutil/openbsd.py	23.37% <0.00%> (+1.24%)	⬆️
azurelinuxagent/common/osutil/openwrt.py	37.80% <0.00%> (+0.45%)	⬆️
azurelinuxagent/common/osutil/redhat.py	58.44% <0.00%> (ø)
azurelinuxagent/common/osutil/ubuntu.py	68.83% <ø> (+0.41%)	⬆️
.../common/protocol/metadata_server_migration_util.py	100.00% <ø> (ø)
azurelinuxagent/common/osutil/gaia.py	27.14% <7.69%> (-2.09%)	⬇️
azurelinuxagent/common/osutil/suse.py	63.63% <21.73%> (-2.04%)	⬇️
azurelinuxagent/common/osutil/iosxe.py	42.10% <28.57%> (+0.92%)	⬆️
... and 41 more

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