Fix SDK constraint (#29)

diff --git a/pubspec.yaml b/pubspec.yaml
index a80a13e..e415e6c 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,9 +1,9 @@
 name: fixnum
-version: 0.10.6
+version: 0.10.7-dev
 author: Dart Team <misc@dartlang.org>
 description: Library for 32- and 64-bit signed fixed-width integers.
 homepage: https://github.com/dart-lang/fixnum
 dev_dependencies:
   test: ^0.12.0
 environment:
-  sdk: ">=1.8.3 <2.0.0-dev.infinity"
+  sdk: ">=1.8.3 <2.0.0"