fixed: plot style with 'legend_outside=False' #476

Job	Run time
conda install (ubuntu-20.04)	5m 2s
Build documentation	2m 20s
Unit tests (ubuntu-20.04, 3.7)	19m 45s
conda install latest tensorflow (ubuntu-20.04)	19m 42s
Unit tests (macos-11, 3.7)	24m 26s
Unit tests (ubuntu-20.04, 3.6)	17m 13s
Unit tests (ubuntu-20.04, 3.8)	14m 52s
Test uproot3 (ubuntu-20.04, 3.7)	23m 1s
Style checks	3m 19s
Coverage (ubuntu-20.04, 3.7)	14s
	2h 9m 54s

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