2015: gogo.slide: correct link to grind

Change-Id: I61737b3bc156221bf139e67b0a1a804c2781cbf9
Reviewed-on: https://go-review.googlesource.com/10368
Reviewed-by: Andrew Gerrand <adg@golang.org>

2015/gogo.slide

diff --git a/2015/gogo.slide b/2015/gogo.slide
index 2670fd6..5fea198 100644
--- a/2015/gogo.slide
+++ b/2015/gogo.slide
@@ -175,8 +175,8 @@
 - removes gotos
 - removes unused labels, needless indirections, etc.
 - moves `var` declarations nearer to first use
-		
-.link rsc.io/grind
+
+.link http://rsc.io/grind
 
 * Performance problems