Fix multiple version bumps when publishing using Yarn

[itaisteinherz]

Fixes #387

// cc @edsrzf @minosss

[sindresorhus]

Can you explain the fix?

[itaisteinherz]

@sindresorhus Running yarn publish --new-version [increment] bumps the package's version several times in addition to the bump that already occurs in the Bump version using ... task. This is what causes the issue described in #387 (at least when testing locally).

[sindresorhus]

I don't use Yarn, so I don't know how it works, but if you've tested it locally, that's good enough for me.

[sindresorhus]

// @ianwalter I think this issue was introduced in add1387