No warning or indication on fail

[Gruski]

Whenever the minifier fails for whatever reason the plugin gives no warning or indication that this occured causing files to no longer be in sync.

For example, the min file compiled fine in previous runs but one day an unparsable, but valid, code snipit is introduced that tests fine in the non-min version but the min version failed to be updated because of said parse error. Now the min production version is out of sync with the normal version being tested in dev. Production will now have errors not present in dev unbeknownst to the developer.

There needs to be a notification of failure that states files are no longer in sync.