tracker-extract: add application/msword to msoffice rules

[tracker] Fix indexing MS Word documents

Identified by functional-tests/400-extractor.py, case office-doc.

This ugly mime type has been misidentified as useless in scope of
GB#733317 and removed with f04b2de (tracker-extract: remove
application/vnd.ms-* catchall from msoffice). Still it is the mime type
returned by libmagic - the result is contents of (some?) doc files are
never extracted.