Allow SDK versions <3.0.0 (#21)

CHANGELOG.md

+# 0.9.6+2
+
+- Set max SDK version to `<3.0.0`, and adjust other dependencies.
+
 # 0.9.6+1
 
 - Stop using deprecated constants from the SDK.

pubspec.yaml

 name: mime
-version: 0.9.6+1
-author: Dart Team <misc@dartlang.org>
+version: 0.9.6+2
+
 description: Helper-package for working with MIME.
+author: Dart Team <misc@dartlang.org>
 homepage: https://www.github.com/dart-lang/mime
+
 environment:
-  sdk: '>=2.0.0-dev.20.0 <2.0.0'
+  sdk: '>=2.0.0-dev.20.0 <3.0.0'
+
 dev_dependencies:
-  test: '^0.12.0'
+  test: ^1.2.0