webpack-jumpstart: stop using git-fsck
webpack-jumpstart: stop using git-fsck

Just like 29fe9c30c5dac8b348ec1ab5c1c625aebc601037 did for git-utils,
use git-rev-list instead of git-fsck.

martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit