OWNERS: switch 'matches' to 'matchers'

The original OWNERS template had a mistake which used 'matches' instead
of the field supported by the Gerrit plugin 'matchers'.  Update the
OWNERS file to have the correct field.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Id3e3eede2419b5b106cbedd10e75c654154bd343