[now dev] Allow a builder `watch` array to contain "./" prefixed paths (#2217)
[now dev] Allow a builder `watch` array to contain "./" prefixed paths (#2217)

The file watcher logic expects that there is no `'./'` prefix on the
watched file paths/patterns, but `path.dirname('foo')` returns `'.'`
which turns into `'./foo'` with `path.join()`. So this allows those
file paths to be returned from the builder and `now dev` normalizes the
paths after the build has completed.
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