doc: remove completed TODO

pretty/doc.go

diff --git a/pretty/doc.go b/pretty/doc.go
index 03b5718..c7b4356 100644
--- a/pretty/doc.go
+++ b/pretty/doc.go
@@ -20,6 +20,3 @@
 //
 // See the Reflect and Print examples for what the output looks like.
 package pretty
-
-// TODO:
-//   - Catch cycles