package.json: bump engines.node version to >=14 (#41599)

Bump the mininum required Node version for the project in package.json's engines property. The version requirement had been left at >=10.0.0, despite the de facto requirement of 14+, as seen in .nvmrc.

package.json

@@ -15,7 +15,7 @@
 		"url": "https://github.com/WordPress/gutenberg/issues"
 	},
 	"engines": {
-		"node": ">=10.0.0",
+		"node": ">=14.0.0",
 		"npm": ">=6.9.0 <7"
 	},
 	"config": {