CommonMistakes: change title

The x/website tests look for the space.

Change-Id: I9dfa025acac6f7f44d03fd9743a485641ab4a3d6
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/550155
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/CommonMistakes.md b/CommonMistakes.md
index 03dbd08..8449ad2 100644
--- a/CommonMistakes.md
+++ b/CommonMistakes.md
@@ -1,5 +1,5 @@
 ---
-title: CommonMistakes
+title: Common Mistakes
 ---
 
 Table of Contents