Support new ErrorStr API in tinyxml2 6.0.0

[jslee02]

There were API breaking changes in tinyxml2 6.0.0. This PR adds band-aid to support tinyxml2 6.0.0 and less.

Referenced https://bitbucket.org/ignitionrobotics/ign-common/pull-requests/87/support-new-errorstr-api-in-tinyxml2-600/diff

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Before creating a pull request

• Document new methods and classes (N/A)
• Format code with make format

Before merging a pull request

• Set version target by selecting a milestone on the right side
• Summarize this change in CHANGELOG.md
• Add unit test(s) for this change (N/A)

[codecov]

Codecov Report

Merging #290 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #290      +/-   ##
==========================================
+ Coverage   80.25%   80.26%   +0.01%     
==========================================
  Files         195      195              
  Lines        5671     5671              
==========================================
+ Hits         4551     4552       +1     
+ Misses       1120     1119       -1

Impacted Files	Coverage Δ
src/io/CatkinResourceRetriever.cpp	74.79% <ø> (ø)	⬆️
src/planner/ompl/CRRT.cpp	76.16% <0%> (+0.58%)	⬆️