Multipart size properties have incorrect suffix

[Javadoc for MultipartProperties](http://docs.spring.io/spring-boot/docs/1.4.2.RELEASE/api/org/springframework/boot/autoconfigure/web/MultipartProperties.html) says that maximum sizes are `1Mb` and `10Mb`. Same values are shown as default values when autocompleting with IDEA.

However, `Mb` means megabits and not megabytes. Correct suffix for megabytes would be either `MB` or `MiB`.