remove trailing whitespace (#9)

diff --git a/docs/writing_stardoc.md b/docs/writing_stardoc.md
index ee76029..fa9cf06 100644
--- a/docs/writing_stardoc.md
+++ b/docs/writing_stardoc.md
@@ -58,7 +58,7 @@
 <a name="provider-documentation"></a>
 ## Provider Documentation
 
-[Starlark Providers](https://docs.bazel.build/versions/master/skylark/rules.html#providers) 
+[Starlark Providers](https://docs.bazel.build/versions/master/skylark/rules.html#providers)
 are documented similarly to rules: using docstrings specified as parameters during
 creation of the provider.