Remove version from pubspec (#1)

Not meant to be published
diff --git a/pubspec.yaml b/pubspec.yaml
index 1bf3f36..b8bf9cc 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,4 @@
 name: observatory
-version: 1.6.0-dev.1
 transformers:
 - dart_to_js_script_rewriter
 - $dart2js: