Fix some minor lint bugs in `completer.lua`
Fix some minor lint bugs in `completer.lua`

Summary: doesexactlywhatitsaysonthetin

Test Plan: By inspection

Reviewed By: tudorb@fb.com

FB internal diff: D1658250

Tasks: 5539137

Signature: t1:1658250:1415134573:b8c1313a28c2cc67bf9368b6217fe75e694acd8a

facebook/fblualib,soumith/fblualib,raphaelamorim/fblualib,facebook/fblualib,szagoruyko/fblualib,raphaelamorim/fblualib,szagoruyko/fblualib,soumith/fblualib