Migrate from no-implicit-casts to strict-casts (dart-lang/pool#60)

diff --git a/pkgs/pool/analysis_options.yaml b/pkgs/pool/analysis_options.yaml
index 4fa4b8d..055ac10 100644
--- a/pkgs/pool/analysis_options.yaml
+++ b/pkgs/pool/analysis_options.yaml
@@ -1,5 +1,5 @@
 include: package:lints/recommended.yaml
 
 analyzer:
-  strong-mode:
-    implicit-casts: false
+  language:
+    strict-casts: true