package.json: Use UI5 Builder PoC feature branch

Author: RandomByte

package.json

@@ -101,7 +101,7 @@
 		"url": "[email protected]:SAP/ui5-cli.git"
 	},
 	"dependencies": {
-		"@ui5/builder": "^1.4.0",
+		"@ui5/builder": "SAP/ui5-builder#feature-proxy",
 		"@ui5/fs": "^1.1.2",
 		"@ui5/logger": "^1.0.1",
 		"@ui5/project": "SAP/ui5-project#feature-proxy",