Merge pull request #284 from mapbox/rl/update_sdk_requirement_in_pubspec

Update dart sdk requirement

Author: evil159

pubspec.yaml

@@ -4,7 +4,7 @@ version: 0.5.0
 homepage: https://github.com/mapbox/mapbox-maps-flutter
 
 environment:
-  sdk: ">=2.19.0 <3.0.0"
+  sdk: ">=2.19.0 <4.0.0"
   flutter: ">=2.0.0"
 
 dependencies: