message: fix user autocomplete not adding `: ` if at the start
diff: @@ -111,7 +111,7 @@ export default class UserProvider extends AutocompleteProvider {
  // relies on the length of the entity === length of the text in the decoration.
  completion: user.rawDisplayName.replace(' (IRC)', ''),
  completionId: user.userId,
  - suffix: (selection.beginning && selection.start === 0) ? ': ' : ' ',
  + suffix: (selection.beginning && range.start === 0) ? ': ' : ' ',
  href: makeUserPermalink(user.userId),
  component: (
  <PillCompletion
  