Description
After upgrading to Metalsmith 2.5.0, we're now getting the error:

TypeError: gen.next is not a function

When metalsmith-watch is triggered in response to a file change.

Environment

• OS (run node -e "console.log(process.platform)"): MacOS
• Node|npm version (run node -v && npm -v): v16.15.0
  8.5.5
• Metalsmith version: (run npm view metalsmith version): 2.5.0

Reproducing the bug

Further debugging to follow.