primer/octicons v17.4.0 on GitHub

#810 840f4eb Thanks @ashygee! - - modifies tasklist icon proposed in https://github.com/github/primer/issues/746
- adds a new checkbox icon using metaphor from previous tasklist metaphor
#807 d280148 Thanks @edokoa! - Add cache 16px icon
#801 8e5dcfc Thanks @gavinmn! - Save paperclip-16.svg, paperclip-24.svg
#806 27575d0 Thanks @ashygee! - Save git-merge-queue-16.svg
#811 a005869 Thanks @ashygee! - Save command-palette-24.svg, command-palette-16.svg