Update e2e example environment constraint (#26)

* Update e2e example environment constraint

* Update package:test dep, set minimum to 2.0.0
diff --git a/e2e_test/pubspec.yaml b/e2e_test/pubspec.yaml
index f102e3c..d9c3577 100644
--- a/e2e_test/pubspec.yaml
+++ b/e2e_test/pubspec.yaml
@@ -5,4 +5,6 @@
 dev_dependencies:
   cli_util: ^0.1.0
   path: ^1.4.1
-  test: ^0.12.0
+  test: ^1.0.0
+environment:
+  sdk: '>=2.0.0 <3.0.0'