Set Prettier to optional peer dependency

Author: mrmckeb

package.json

@@ -37,5 +37,10 @@
   },
   "peerDependencies": {
     "prettier": ">= 1.16.0"
+  },
+  "peerDependenciesMeta": {
+    "prettier": {
+      "optional": true
+    }
   }
 }