Fixes XGBoost classifier bug with feature names that contain [, ], or <

[angela97lin]

Closes #589

[codecov]

Codecov Report

Merging #659 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #659      +/-   ##
==========================================
+ Coverage   99.06%   99.07%   +0.01%     
==========================================
  Files         139      139              
  Lines        4907     4963      +56     
==========================================
+ Hits         4861     4917      +56     
  Misses         46       46              

Impacted Files	Coverage Δ
...nents/estimators/classifiers/xgboost_classifier.py	100.00% <100.00%> (ø)
...ponents/estimators/regressors/xgboost_regressor.py	100.00% <100.00%> (ø)
evalml/tests/component_tests/test_components.py	100.00% <100.00%> (ø)
...l/tests/component_tests/test_xgboost_classifier.py	100.00% <100.00%> (ø)
...ml/tests/component_tests/test_xgboost_regressor.py	100.00% <100.00%> (ø)

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[dsherry]

Solid start, left some suggestions!

[dsherry]

@angela97lin : heads up @jeremyliweishih is about to add an xgboost regression component and pipeline in #666. If he merges before you do, you'll need to give the regressor the same treatment as the classifier, right? Someone will have to do it either way, haha.

[dsherry]

Left a few more requests, but after that this is ready to go from my perspective!

[dsherry]

@angela97lin I know you're about to merge this (!!!) but reminder to move PRs which are in review to Review/QA

[angela97lin]

@dsherry gotcha, moved!

[dsherry]

@angela97lin I left a couple more suggestions, very close :)

[dsherry]

I think I already approved this but re-approving haha, great stuff!