Disallow self-LGTMs

according opencontainers/project-template#13
we should disallow self-LGTMs

Signed-off-by: Lei Jitang <[email protected]>

Author: coolljt0725

.pullapprove.yml

@@ -2,6 +2,7 @@ approve_by_comment: true
 approve_regex: '^(Approved|lgtm|LGTM|:shipit:|:star:|:\+1:|:ship:)'
 reject_regex: ^Rejected
 reset_on_push: true
+author_approval: ignored
 signed_off_by:
   required: true
 reviewers: