breaking: replace shelljs with fs-extra

[erisu]

Motivation, Context & Description

• Remove shelljs dependency for fs-extra.

Testing

• npm t

Checklist

• I've run the tests to see all new and existing tests pass

[codecov-commenter]

Codecov Report

Merging #851 into master will decrease coverage by 0.08%.
The diff coverage is 76.19%.

@@            Coverage Diff             @@
##           master     #851      +/-   ##
==========================================
- Coverage   74.85%   74.76%   -0.09%     
==========================================
  Files          13       13              
  Lines        1742     1736       -6     
==========================================
- Hits         1304     1298       -6     
  Misses        438      438              

Impacted Files	Coverage Δ
bin/templates/scripts/cordova/lib/run.js	20.72% <0.00%> (-0.71%)	⬇️
bin/templates/scripts/cordova/lib/build.js	50.76% <50.00%> (ø)
...ates/scripts/cordova/lib/plugman/pluginHandlers.js	90.05% <90.90%> (-0.16%)	⬇️
bin/templates/scripts/cordova/lib/check_reqs.js	46.93% <100.00%> (ø)
bin/templates/scripts/cordova/lib/prepare.js	85.67% <100.00%> (-0.04%)	⬇️
bin/templates/scripts/cordova/lib/projectFile.js	94.54% <100.00%> (-0.10%)	⬇️

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[breautek]

LGTM