Bump futures-util from 0.3.4 to 0.3.21 in /frontend#12

dependabot[bot] wants to merge 1 commit intomasterjbowens/covplot:masterfrom

dependabot/cargo/frontend/futures-util-0.3.21jbowens/covplot:dependabot/cargo/frontend/futures-util-0.3.21Copy head branch name to clipboard