Update flutter web samples (#161)

* update gallery and web samples

compatable with SDK version 2a576b774c:

Flutter 1.12.3-pre.38 • channel master • git@github.com:flutter/flutter.git
Framework • revision 2a576b774c (2 hours ago) • 2019-11-15 13:15:05 -0800
Engine • revision b2640d97e7
Tools • Dart 2.7.0

* add preview image

web/slide_puzzle/pubspec.lock

@@ -14,7 +14,7 @@ packages:
       name: archive
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.10"
+    version: "2.0.11"
   args:
     dependency: transitive
     description:
@@ -28,7 +28,7 @@ packages:
       name: async
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.3.0"
+    version: "2.4.0"
   boolean_selector:
     dependency: transitive
     description:
@@ -57,6 +57,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "2.1.1"
+  coverage:
+    dependency: transitive
+    description:
+      name: coverage
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.13.3+1"
   crypto:
     dependency: transitive
     description:
@@ -144,13 +151,6 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "0.6.1+1"
-  json_rpc_2:
-    dependency: transitive
-    description:
-      name: json_rpc_2
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "2.1.0"
   kernel:
     dependency: transitive
     description:
@@ -158,20 +158,27 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "0.3.19"
+  logging:
+    dependency: transitive
+    description:
+      name: logging
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.11.3+2"
   matcher:
     dependency: transitive
     description:
       name: matcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.5"
+    version: "0.12.6"
   meta:
     dependency: transitive
     description:
       name: meta
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.7"
+    version: "1.1.8"
   mime:
     dependency: transitive
     description:
@@ -337,21 +344,21 @@ packages:
       name: test
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.6.3"
+    version: "1.9.4"
   test_api:
     dependency: transitive
     description:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.5"
+    version: "0.2.11"
   test_core:
     dependency: transitive
     description:
       name: test_core
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.5"
+    version: "0.2.15"
   typed_data:
     dependency: transitive
     description:
@@ -366,13 +373,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.8"
-  vm_service_client:
+  vm_service:
     dependency: transitive
     description:
-      name: vm_service_client
+      name: vm_service
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.6+3"
+    version: "2.1.1"
   watcher:
     dependency: transitive
     description: