don't attempt to handle non-files

Before something like...

```javascript
filerev: {
	predeploy: {
		src: 'deploy/assets/**/*'
	}
},
```

would get caught on a folder and break with an error like

```
Warning: Unable to read "deploy/assets/compiled" file (Error code: EISDIR). Use --force to continue.
```

BUT NO LONGER :horse: