message: Add "language_override" option to index options
  types(src): IndexOptions add "language_override"
  fixes typegoose/typegoose#223
diff: @@ -408,6 +408,7 @@ export interface IndexOptions<T> {
  partialFilterExpression?: any;
  collation?: object;
  default_language?: string;
  + language_override?: string;
  lowercase?: boolean; // whether to always call .toLowerCase() on the value
  uppercase?: boolean; // whether to always call .toUpperCase() on the value
  