Properly depend on async.

We had this as a dev dependency, but we were importing it from lib.

R=jmesserly@google.com

Review URL: https://codereview.chromium.org//2074573002 .

pkgs/http_multi_server/CHANGELOG.md

diff --git a/pkgs/http_multi_server/CHANGELOG.md b/pkgs/http_multi_server/CHANGELOG.md
index 198b1b6..5e45056 100644
--- a/pkgs/http_multi_server/CHANGELOG.md
+++ b/pkgs/http_multi_server/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 2.0.2
+
+* Fix a dependency that was incorrectly marked as dev-only.
+
 ## 2.0.1
 
 * Fix most strong mode errors and warnings.

pkgs/http_multi_server/pubspec.yaml

diff --git a/pkgs/http_multi_server/pubspec.yaml b/pkgs/http_multi_server/pubspec.yaml
index 647b7eb..37bb75e 100644
--- a/pkgs/http_multi_server/pubspec.yaml
+++ b/pkgs/http_multi_server/pubspec.yaml
@@ -1,11 +1,12 @@
 name: http_multi_server
-version: 2.0.1
+version: 2.0.2
 author: "Dart Team <misc@dartlang.org>"
 homepage: http://github.com/dart-lang/http_multi_server
 description:
   A dart:io HttpServer wrapper that handles requests from multiple servers.
-dev_dependencies:
+dependencies:
   async: "^1.2.0"
+dev_dependencies:
   test: ">=0.12.0 <0.13.0"
   http: ">=0.11.0 <0.12.0"
 environment: