sometimes you need to burn your builder

Added npm shortcut to blow away backstopbuilder.  Run this and reinit as needed.

package.json

@@ -42,6 +42,7 @@
     "publish-docker": "PV=$(node -p -e \"require('./package.json').version\"); echo $PV; docker buildx build --push --platform linux/amd64,linux/arm64 -t backstopjs/backstopjs:$PV --build-arg BACKSTOPJS_VERSION=$PV docker; docker buildx build --push --platform linux/amd64,linux/arm64 -t backstopjs/backstopjs:latest --build-arg BACKSTOPJS_VERSION=$PV docker",
     "build-and-publish": "npm run publish-npm && npm run build-docker && npm run publish-docker",
     "init-docker-builder": "docker buildx create --name backstopbuilder --use --bootstrap",
+    "burn-docker-builder": "docker buildx rm backstopbuilder",
     "success-message": "printf \"\\n\\e[32m✓ SUCCESS!\\e[0m BackstopJS internal testing passed.\\n\"",
     "caution-message": "printf \"\\n\\e[33m⚠ Notice.\\e[0m BackstopJS internal testing exited with a non-success status. This is expected when BackstopJS finds differences.\\n\"",
     "fail-message": "printf \"\\n\\e[31m✖ FAIL!\\e[0m BackstopJS internal testing failed. See logs for details.\\n\""