Add an SDK constraint to allow using "^" dependencies.
diff --git a/pubspec.yaml b/pubspec.yaml
index ab2e774..3d89180 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -3,6 +3,8 @@
 author: Dart Team <misc@dartlang.org>
 description: Opinionated, automatic Dart source code formatter.
 homepage: https://github.com/dart-lang/dart_style
+environment:
+  sdk: ">=1.8.0 <2.0.0"
 dependencies:
   analyzer: '>=0.25.0 <=0.26.0-alpha.0'
   args: '>=0.12.1 <0.14.0'
@@ -16,7 +18,6 @@
 executables:
   dartfmt: format
   dartformat: format # Allow the old name for compatibility.
-
 # Tell the bots not to bother building the tests since they don't run in a
 # browser anyway.
 transformers: