express-openapi media type mismatch due to charset directive

[alextes]

For openapi 3.0.1 , sending a POST with a Content-Type header set to application/json; charset=utf-8 fails with a Request Body Object content property set to application/json due to the charset directive, resulting in a 415 response. I'm guessing a === string comparison is happening somewhere on the full header rather than just the media-type in the Content-Type header.

[jsdevel]

@alextes please open a PR