Fix documentation for the 'name' metadata field

Fix documentation for the 'name' metadata field

The metadata field for a file path is "name", but the format
documentation incorrectly says it is "path".

Original versions of Cumulus used "name".  Commit 6c94114148c4 renamed
this to "path" (and updated the documentation), but the naming change
was later reverted in commit 03e760560aa7 (since the benefits weren't
deemed worth the potential complexity of supporting both names).  This
happened between the v0.5.1 and v0.6 releases but was never in any
released code.

The naming revert updated code but forgot to revert the documentation
change.  Fix that.