message: Fix DocumentSymbol.is: detail is optional
diff: @@ -1698,8 +1698,9 @@ export namespace DocumentSymbol {
  export function is(value: any): value is DocumentSymbol {
  let candidate: DocumentSymbol = value;
  return candidate &&
  - Is.string(candidate.name) && Is.string(candidate.detail) && Is.number(candidate.kind) &&
  + Is.string(candidate.name) && Is.number(candidate.kind) &&
  Range.is(candidate.range) && Range.is(candidate.selectionRange) &&
  + (candidate.detail === void 0 || Is.string(candidate.detail)) &&
  (candidate.deprecated === void 0 || Is.boolean(candidate.deprecated)) &&
  (candidate.children === void 0 || Array.isArray(candidate.children));
  }
  