Update pubspec.yaml

Updated Pubspec.yaml to accept higher versions of Http package to prevent below error message when installing.

pubspec.yaml

@@ -20,7 +20,7 @@ dependencies:
   file: ">=6.1.4 <8.0.0"
   path: ^1.8.3
   args: ^2.4.0
-  http: ^0.13.6
+  http: ">=0.13.6 <1.2.3"
   meta: ^1.10.0
   process: ^5.0.0
   unified_analytics: ">=5.8.0 <7.0.0"