THRIFT-3981 Enable analyzer strong mode in Dart library
Client: Dart
Patch: Mark Erickson <merickson@apache.org>

This closes #1135
diff --git a/lib/dart/.analysis_options b/lib/dart/.analysis_options
new file mode 100644
index 0000000..a10d4c5
--- /dev/null
+++ b/lib/dart/.analysis_options
@@ -0,0 +1,2 @@
+analyzer:
+  strong-mode: true