fix(package.json): add package.json to exports

If you are using bundlers like metro in rn-native (or tools that make use of metainformation of packages) you will recieve an import warning like:
```
warn Package pretty-bytes has been ignored because it contains invalid configuration. Reason: Package subpath './package.json' is not defined by "exports" in /Users/****/Applications/****/****/app/node_modules/pretty-bytes/package.json
```

There was a similar Issue in `uuidjs`, for discussion you can see this issue uuidjs/uuid#444 (comment)

package.json

@@ -11,7 +11,10 @@
 		"url": "https://sindresorhus.com"
 	},
 	"type": "module",
-	"exports": "./index.js",
+	"exports": {
+    		".": "./index.js",
+    		"./package.json": "./package.json"
+  	},
 	"types": "./index.d.ts",
 	"engines": {
 		"node": "^14.13.1 || >=16.0.0"