Format strings are not substituted in error message

[jdbaldry]

I expected that usage of %q or other format strings would result in the error message substituting those for the arguments defined in args.

Concrete example using eish serve, built at the latest release, on a .go file to trigger an error with format strings.
Errata source at 39fda0b:

$ eish serve --source ~/ext/dannykopping/errata/errata.go

Returns:

eish encountered an error: [errata-serve-web-ui] <[email protected]/command.go:163> Cannot serve web UI for datasource %q (path="/home/jdb/ext/dannykopping/errata/errata.go"). For more details, see https://dannykopping.github.io/errata/errata/errata-serve-web-ui
...

I expected something like:

eish encountered an error: [errata-serve-web-ui] <[email protected]/command.go:163> Cannot serve web UI for datasource "/home/jdb/ext/dannykopping/errata/errata.go". For more details, see https://dannykopping.github.io/errata/errata/errata-serve-web-ui
...