Migrate from no-implicit-casts to strict-casts (#66)

analysis_options.yaml

diff --git a/analysis_options.yaml b/analysis_options.yaml
index c4dc6ae..acc502f 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -1,8 +1,8 @@
 include: package:lints/recommended.yaml
 
 analyzer:
-  strong-mode:
-    implicit-casts: false
+  language:
+    strict-casts: true
 
 linter:
   rules: