message: Use scope support.class.key for keys in bib files
  This scope seems better customized by standard themes than
  support.variable.
diff: <key>1</key>
  <dict>
  <key>name</key>
  - <string>support.variable.key.bibtex</string>
  + <string>support.function.key.bibtex</string>
  </dict>
  <key>2</key>
  <dict>
  <key>1</key>
  <dict>
  <key>name</key>
  - <string>support.variable.key.bibtex</string>
  + <string>support.function.key.bibtex</string>
  </dict>
  <key>2</key>
  <dict>
  