InstallTroubleshooting: correct table of contents

Change-Id: I39a39a364dfc9a785eb3af758e4826b9495719f0
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/623696
Commit-Queue: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
diff --git a/InstallTroubleshooting.md b/InstallTroubleshooting.md
index b095460..23b3731 100644
--- a/InstallTroubleshooting.md
+++ b/InstallTroubleshooting.md
@@ -9,8 +9,7 @@
 ## Contents
   * [Introduction](#introduction)
   * [Tips](#tips)
-    * [Environment](#environment)
-    * [GOROOT vs GOPATH](#goroot-vs-gopath)
+    * [Environment variables](#environment-variables)
   * [Troubleshooting](#troubleshooting)
     * [Still need help?](#still-need-help)