message: fix typescript error
  Fix the following typescript error:
  > Type '(conventions: DocumentConventions) => RavenCommand<boolean>' is
  not assignable to type '(conventions: DocumentConventions) =>
  RavenCommand<Boolean>'.
  > Call signature return types 'RavenCommand<boolean>' and
  'RavenCommand<Boolean>' are incompatible.
  > Type 'Boolean' is not assignable to type 'boolean'.
  > 'boolean' is a primitive, but 'Boolean' is a wrapper object.
diff: @@ -8,7 +8,7 @@ import { HttpRequestParameters } from "../../../Primitives/Http";
  import { HeadersBuilder } from "../../../Utility/HttpUtil";
  import * as stream from "readable-stream";
  -export class IndexHasChangedOperation implements IMaintenanceOperation<Boolean> {
  +export class IndexHasChangedOperation implements IMaintenanceOperation<boolean> {
  private readonly _definition: IndexDefinition;
  