Don't depend on pre-release versions

That was useful when migrating to nnbd but not anymore

pubspec.yaml

@@ -11,13 +11,13 @@ environment:
 dependencies:
   clock: ^1.1.0
   collection: ">=1.15.0 <2.0.0"
-  file: ">=6.0.0-0 <7.0.0"
+  file: ">=6.0.0 <7.0.0"
   flutter:
     sdk: flutter
   flutter_localizations:
     sdk: flutter
-  http: ">=0.13.0-0 <0.15.0"
-  http_parser: ">=4.0.0-0 <5.0.0"
+  http: ">=0.13.0 <0.15.0"
+  http_parser: ">=4.0.0 <5.0.0"
   intl: ">=0.16.0 <2.0.0" # whatever "sdk: flutter" depends on
   material_color_utilities: ">=0.1.2 <1.0.0"
   path_provider: ">=2.0.0 <3.0.0"