Build favicons locally #568

Job	Run time
R-CMD-check / macOS-latest (release)	6m 16s
R-CMD-check / windows-latest (devel)	8m 40s
R-CMD-check / windows-latest (release)	6m 59s
R-CMD-check / windows-latest (oldrel)	6m 51s
R-CMD-check / windows-latest (4.1)	8m 48s
R-CMD-check / ubuntu-latest (devel)	10m 50s
R-CMD-check / ubuntu-latest (release)	9m 8s
R-CMD-check / ubuntu-latest (4.3)	10m 49s
R-CMD-check / ubuntu-latest (4.2)	10m 49s
R-CMD-check / ubuntu-latest (4.1)	7m 46s
R-CMD-check / ubuntu-latest (4.0)	2m 57s
R-CMD-check / ubuntu-latest (3.6)	2m 50s
	1h 32m 43s

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