new IANA extensions for application/mp4 break existing mp4 -> video/mp4 mapping

[broofa]

As reported in broofa/mime#297.

This commit in mime-db added mp4 as an extension for the application/mp4 type. This created a conflict with the existing (and long-established) mp4 extension in the video/mp4 type (also defined by IANA!). Because this module gives higher precedence to application types than default types, it has caused the mapping to change between mime@3 and mime@4.

Note: Prioritizing audio and video over application appears to fix this problem with minimal impact on other type mappings. PR forthcoming.

cc: @dougwilson for possible issue with mime-types.