Migrate from no-implicit-casts to strict-casts (dart-lang/stream_transform#161)

pkgs/stream_transform/analysis_options.yaml

diff --git a/pkgs/stream_transform/analysis_options.yaml b/pkgs/stream_transform/analysis_options.yaml
index 0256c70..6af98d7 100644
--- a/pkgs/stream_transform/analysis_options.yaml
+++ b/pkgs/stream_transform/analysis_options.yaml
@@ -1,9 +1,8 @@
 include: package:lints/recommended.yaml
 
 analyzer:
-  strong-mode:
-    implicit-casts: false
   language:
+    strict-casts: true
     strict-raw-types: true
 
 linter: