Remove deprecations warnings

[Zlopez]

Remove deprecations warnings from tests.

WTForms:

• TextField alias
• Required field option

Python 3.6:

• regular expression warnings (using escape sequence within utf string, using flag inside regex)

XML2Dict:

• getchildren method

What remains:

• fedmsg related warnings - these are inside fedmsg

[codecov-io]

Codecov Report

Merging #627 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #627   +/-   ##
=======================================
  Coverage   90.05%   90.05%           
=======================================
  Files          55       55           
  Lines        2655     2655           
  Branches      343      343           
=======================================
  Hits         2391     2391           
  Misses        201      201           
  Partials       63       63

Impacted Files	Coverage Δ
anitya/config.py	100% <ø> (ø)	⬆️
anitya/lib/backends/debian.py	100% <ø> (ø)	⬆️
anitya/lib/xml2dict.py	85.41% <100%> (ø)	⬆️
anitya/forms.py	81.57% <100%> (ø)	⬆️

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