Allow for the PluginError constructor to be called without new.

[dead-claudia]

This also falls in line with the builtin Error types and most of the other builtins as well.

[coveralls]

Coverage remained the same when pulling 4e124b9 on impinball:master into fb4df4b on gulpjs:master.

[coveralls]

Coverage remained the same when pulling d528546 on impinball:master into fb4df4b on gulpjs:master.

[sindresorhus]

👎 It should be explicit that it's a new instance.

[yocontra]

This will add a new item to the error stack and push other stuff off. You can manipulate the stack to remove PluginError from it

[phated]

Closing, as work shouldn't be done in this module anymore.