Update @rollup/pluginutils to latest version

[TerryRPatterson]

This improves the include/excludes and allows matching of files not in process.cwd()
This contains 3 breaking changes in @ollup/pluginutils:

• fix(pluginutils)!: don't add cwd to absolute or patterns that start with a glob rollup/plugins#517
• Minimum compatible Rollup version is 1.20.0
• Minimum supported Node version is 8.0.0

Since we only use filter, and it doesn't use much of node, or rollup I think only the first breaking change will have much of an effect on our users.

[malchata]

I brought this in and updated all dependencies. I published a new version (0.5.0) under the next tag on npm, so to test this, you'll need to reference it explicitly on install:

npm i rollup-plugin-imagemin@next

If you're satisfied, I'll republish without the next tag. Sorry for the delay, I was subscribed to some repos that were burying me in notifications and some housekeeping on my own stuff got lost in the mix.

[TerryRPatterson]

The issue is fixed, thanks!