THRIFT-4654 Minor fixes for dart 1 & 2 compatibility (backwards compatible) (#1617)
* THRIFT-4654 Minor fixes for dart 1 & 2 compatibility
* update dockerfiles for CI to test dart 2
* THRIFT-4654 update pubspec for tests
* THRIFT-4654 update dart test generator and readme to 1.24.3
* THRIFT-4654 update generated dart sdk to a range
* fix the dart tutorials
* Add .dart_tool directories to .gitignore
* THRIFT-4654: use dart 2.1.0 and fix cross test dart client timeout
diff --git a/lib/dart/README.md b/lib/dart/README.md
index 2be168b..4c30291 100644
--- a/lib/dart/README.md
+++ b/lib/dart/README.md
@@ -23,4 +23,4 @@
Using Thrift with Dart
====================
-Dart 1.12.0 or newer is required
+Dart 1.24.3 or newer is required