prop-types should be a proper dependency

[magnattic]

Right now prop-types is a devDependency even though it is needed by the package to run properly. This breaks the package when used with yarn 3 and plug'n'play, because prop-types will not be installed with google-maps-react and consecutively not accessible:

ModuleNotFoundError: Module not found: Error: Can't resolve 'prop-types' in '/srv/.yarn/virtual/google-maps-react-virtual-a5292661de/0/cache/google-maps-react-npm-2.0.6-79c5177d9a-cf5120d6ff.zip/node_modules/google-maps-react/dist/components'