design: 47781-parameterized-go-ast.md: remove back-ticks from title

I just noticed this causes the package paths to be elided from the page
title in my tab bar.

Change-Id: I9706cf8e704ae8f4f3c2f3fe32f5b739ded5a55d
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/343229
Reviewed-by: Robert Findley <rfindley@google.com>

design/47781-parameterized-go-ast.md

diff --git a/design/47781-parameterized-go-ast.md b/design/47781-parameterized-go-ast.md
index 49f453a..ac470e2 100644
--- a/design/47781-parameterized-go-ast.md
+++ b/design/47781-parameterized-go-ast.md
@@ -1,4 +1,4 @@
-# Additions to `go/ast` and `go/token` to support parameterized functions and types
+# Additions to go/ast and go/token to support parameterized functions and types
 
 Authors: Rob Findley, Robert Griesemer