pubspec didn't have 0.9.13 in it (#1357)

Author: jcollins-g

pubspec.yaml

@@ -1,6 +1,6 @@
 name: dartdoc
 # Also update the `version` field in lib/dartdoc.dart.
-version: 0.9.12
+version: 0.9.13
 author: Dart Team <[email protected]>
 description: A documentation generator for Dart.
 homepage: https://github.com/dart-lang/dartdoc