Fix duplicate dependency on string_scanner

Author: kevmoo

pubspec.yaml

@@ -1,13 +1,12 @@
 name: http_parser
-version: 3.0.2
+version: 3.0.3
 author: "Dart Team <misc@dartlang.org>"
 homepage: https://github.com/dart-lang/http_parser
 description: >
   A platform-independent package for parsing and serializing HTTP formats.
 dependencies:
   collection: ">=0.9.1 <2.0.0"
   source_span: "^1.0.0"
-  string_scanner: ">=0.0.0 <0.2.0"
   string_scanner: ">=0.0.0 <2.0.0"
 dev_dependencies:
   test: "^0.12.0"