go/ast: fix comment formatting

A bullet list was getting mangled in godoc.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/13060047

src/pkg/go/ast/commentmap.go

@@ -129,11 +129,11 @@ func (s *nodeStack) pop(pos token.Pos) (top Node) {
 //
 // A comment group g is associated with a node n if:
 //
-// - g starts on the same line as n ends
-// - g starts on the line immediately following n, and there is
-//   at least one empty line after g and before the next node
-// - g starts before n and is not associated to the node before n
-//   via the previous rules
+//   - g starts on the same line as n ends
+//   - g starts on the line immediately following n, and there is
+//     at least one empty line after g and before the next node
+//   - g starts before n and is not associated to the node before n
+//     via the previous rules
 //
 // NewCommentMap tries to associate a comment group to the "largest"
 // node possible: For instance, if the comment is a line comment