use latest dart sdk version

Author: lohanidamodar

templates/dart/pubspec.yaml.twig

@@ -6,7 +6,7 @@ repository: https://github.com/{{sdk.gitUserName}}/{{sdk.gitRepoName}}
 issue_tracker: https://github.com/appwrite/sdk-generator/issues
 documentation: {{ spec.contactURL }}
 environment:
-  sdk: '>=2.14.0 <3.0.0'
+  sdk: '>=2.17.0 <3.0.0'
 dependencies:
   http: ^0.13.4
 

templates/flutter/pubspec.yaml.twig

@@ -6,7 +6,7 @@ repository: https://github.com/{{sdk.gitUserName}}/{{sdk.gitRepoName}}
 issue_tracker: https://github.com/appwrite/sdk-generator/issues
 documentation: {{ spec.contactURL }}
 environment:
-  sdk: '>=2.14.0 <3.0.0'
+  sdk: '>=2.17.0 <3.0.0'
 dependencies:
   flutter:
     sdk: flutter