Fixes bug in outlier plot method #1068

Job	Run time
R-CMD-check / macOS-latest (release)	12m 21s
R-CMD-check / windows-latest (devel)	16m 46s
R-CMD-check / windows-latest (release)	27m 16s
R-CMD-check / windows-latest (oldrel)	24m 40s
R-CMD-check / ubuntu-latest (devel)	1h 37m 43s
R-CMD-check / ubuntu-latest (release)	21m 28s
R-CMD-check / ubuntu-latest (oldrel)	17m 58s
R-CMD-check / ubuntu-latest (oldrel-2)	2m 35s
R-CMD-check / ubuntu-latest (oldrel-3)	2m 43s
R-CMD-check / ubuntu-latest (3.6)	2m 33s
	3h 46m 3s

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