DocsKeyboardShortcutsComponent: pressing 'g' key throws TypeError

[geneukum]

When I run the ember-intl docs app locally (uses v5.0.0 of ember-cli-addon-docs) and then press the 'g' key, I see an error logged to the console:

Uncaught TypeError: this.set is not a function
    at ClassAsKeyResponder.goto (index.js:247:1)
    at eval (handle-key-event.js:16:1535)
    at Array.forEach (<anonymous>)
    at triggerResponderListener (handle-key-event.js:16:1354)
    at handleKeyEventWithPropagation (handle-key-event.js:16:897)
    at eval (keyboard.js:29:1907)
    at Backburner._run (backburner.js:1052:1)
    at Backburner.run (backburner.js:773:1)
    at run (index.js:83:1)
    at KeyboardService._respond (keyboard.js:29:1769)

This makes sense, since DocsKeyboardShortcutsComponent is a glimmer component which won't have this.set available. I think that we can probably just switch this over to a regular assignment to avoid the problem.