Fix server-communication example compile-time error

[GZGavinZhao]

Up for grabs issue. Probably an easy fix, but I'm focusing on migrating examples to git submodules now, so just putting it here in case someone has the time for it.

Analyzing server-communication...      3.9s

  error • lib/src/toh/hero_service.dart:23:40 • The argument type 'String' can't be assigned to the parameter type 'Uri'. • argument_type_not_assignable
  error • lib/src/toh/hero_service.dart:38:41 • The argument type 'String' can't be assigned to the parameter type 'Uri'. • argument_type_not_assignable
  error • lib/src/wiki/wiki_smart_component.dart:27:20 • The method 'debounce' isn't defined for the type 'WikiSmartComponent'. Try correcting the name to the name of an existing method, or defining a method named 'debounce'. •
          undefined_method
  error • lib/src/wiki/wiki_smart_component.dart:30:13 • The method 'switchMap' isn't defined for the type 'WikiSmartComponent'. Try correcting the name to the name of an existing method, or defining a method named 'switchMap'. •
          undefined_method
   info • lib/src/wiki/wiki_smart_component.dart:3:8 • Unused import: 'package:stream_transform/stream_transform.dart'. Try removing the import directive. • unused_import

5 issues found.

Instructions:

1. Clone angulardart-community/server-communication. Create a PR there that fixes the issue. Reference this issue in that PR. Also ignore the README.
2. (Optional, I can do this) After that PR has been merged, in this repo, run git submodule update --remote --merge. If this doesn't work, search for "how to update git submodules". After that, commit the new changes in this repo (git add --all && git commit) and submit a PR to this repo.