fix web plugin issue

example/.flutter-plugins-dependencies

@@ -1 +1 @@
-{"info":"This is a generated file; do not edit or check into version control.","plugins":{"ios":[{"name":"hexcolor","path":"/media/ggriffo/mystuff/alinuxfl/projects/hexcolor/","dependencies":[]}],"android":[{"name":"hexcolor","path":"/media/ggriffo/mystuff/alinuxfl/projects/hexcolor/","dependencies":[]}],"macos":[],"linux":[],"windows":[],"web":[]},"dependencyGraph":[{"name":"hexcolor","dependencies":[]}],"date_created":"2020-10-09 20:33:35.472204","version":"1.23.0-8.0.pre.259"}
+{"info":"This is a generated file; do not edit or check into version control.","plugins":{"ios":[{"name":"hexcolor","path":"/media/ggriffo/mystuff/alinuxfl/projects/hexcolor/","dependencies":[]}],"android":[{"name":"hexcolor","path":"/media/ggriffo/mystuff/alinuxfl/projects/hexcolor/","dependencies":[]}],"macos":[],"linux":[],"windows":[],"web":[]},"dependencyGraph":[{"name":"hexcolor","dependencies":[]}],"date_created":"2020-10-09 20:50:33.268697","version":"1.23.0-8.0.pre.259"}

pubspec.lock

@@ -60,6 +60,18 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_web_plugins:
+    dependency: "direct dev"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
+  js:
+    dependency: transitive
+    description:
+      name: js
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.6.3-nullsafety.1"
   matcher:
     dependency: transitive
     description:

pubspec.yaml

@@ -16,6 +16,8 @@ dependencies:
 dev_dependencies:
   flutter_test:
     sdk: flutter
+  flutter_web_plugins:
+    sdk: flutter
 
 # The following section is specific to Flutter.
 flutter: