fix(package): add "/src" to files to fix source map warning

Relates to remarkablemark/html-react-parser#1097

```
WARNING in ./node_modules/html-dom-parser/lib/client/constants.js
Module Warning (from ./node_modules/react-scripts/node_modules/source-map-loader/dist/cjs.js):
Failed to parse source map from 'node_modules/html-dom-parser/src/client/constants.ts' file: Error: ENOENT: no such file or directory, open 'node_modules/html-dom-parser/src/client/constants.ts'
```

Author: remarkablemark

package.json

@@ -99,7 +99,8 @@
   "files": [
     "/dist",
     "/esm",
-    "/lib"
+    "/lib",
+    "/src"
   ],
   "browser": {
     "./lib/index.js": "./lib/client/html-to-dom.js",