Fix incorrect path to type definition

version.ts has resolved package.json from project root by. Thus, type
definitions will create based on root directory, not `src` dir. So
`types` field requires adding extra `src` directory.

package.json

@@ -29,7 +29,7 @@
     "node": ">=8.9.0"
   },
   "main": "lib/marp-cli.js",
-  "types": "types/marp-cli.d.ts",
+  "types": "types/src/marp-cli.d.ts",
   "files": [
     "marp-cli.js",
     "lib/",