SpringBoot Upgrade to Embedded Mongo 3.0.0

New version of de.flapdoodle.embed.mongo was released about a month ago. This PR updates Embeded Mongo dependency and updates EmbededMongoAutoconfiguration with new API.

Related: https://github.com/flapdoodle-oss/de.flapdoodle.embed.mongo/issues/325

Comment From: snicoll

@pdambrauskas thank you for making your first contribution to Spring Boot.