Update analysis_options.yaml (dart-lang/web_socket_channel#247)

pkgs/web_socket_channel/analysis_options.yaml

diff --git a/pkgs/web_socket_channel/analysis_options.yaml b/pkgs/web_socket_channel/analysis_options.yaml
index 09635ee..7ac43f4 100644
--- a/pkgs/web_socket_channel/analysis_options.yaml
+++ b/pkgs/web_socket_channel/analysis_options.yaml
@@ -1,8 +1,8 @@
 include: package:pedantic/analysis_options.yaml
 
 analyzer:
-  strong-mode:
-    implicit-casts: false
+  language:
+    strict-casts: true
 
 linter:
   rules: