Move test to dev_dependencies, widen constraint

Author: seaneagan

pubspec.yaml

@@ -10,6 +10,6 @@ dependencies:
   mockable_filesystem: '>=0.0.3 <0.1.0'
   path: '>=1.3.3 <2.0.0'
   supports_color: '>=0.1.1 <0.2.0'
-  test: 0.12.0-beta.3
 dev_dependencies:
   grinder: 0.7.0-dev.1
+  test: '>=0.12.0-beta.3 <0.13.0'