Bump dev dependencies (dart-lang/markdown#573)

pkgs/markdown/pubspec.yaml

diff --git a/pkgs/markdown/pubspec.yaml b/pkgs/markdown/pubspec.yaml
index 2ef835f..c452f4c 100644
--- a/pkgs/markdown/pubspec.yaml
+++ b/pkgs/markdown/pubspec.yaml
@@ -26,9 +26,9 @@
   html: ^0.15.0
   http: ^1.0.0
   io: ^1.0.0
-  js: ^0.6.3
+  js: ^0.7.0
   path: ^1.8.0
   pool: ^1.5.1
-  tar: ^0.5.5+1
+  tar: ^1.0.3
   test: ^1.16.0
   yaml: ^3.0.0