Avoid printing () in certain author-in-text citations.

pandoc --filter pandoc-citeproc -t markdown-citations <<EOT

@doe claims that water is wet.

---
csl: modern-language-association.csl
references:
- title: Title
  id: doe
  issued:
    year: 2013
  author:
    given:
    - John
    family: Doe
  publisher: Publisher
  type: book
  publisher-place: Location
  language: en-US
...
EOT