sdk constraint to 1.8.0
diff --git a/pubspec.yaml b/pubspec.yaml
index 7ed42a8..0a05db1 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -5,7 +5,7 @@
 homepage: https://github.com/dart-lang/pub_cache
 
 environment:
-  sdk: '>=1.0.0 <2.0.0'
+  sdk: '>=1.8.0 <2.0.0'
 
 dependencies:
   path: '^1.0.0'