content: correct mistake in "Slices" article

Change-Id: Ie994d952ff94f05c63fc63389ec359d3e9a902e9
Reviewed-on: https://go-review.googlesource.com/64590
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/content/go-slices-usage-and-internals.article b/content/go-slices-usage-and-internals.article
index d4a50fd..4ba1365 100644
--- a/content/go-slices-usage-and-internals.article
+++ b/content/go-slices-usage-and-internals.article
@@ -190,7 +190,7 @@
 Since the zero value of a slice (`nil`) acts like a zero-length slice, you can declare a slice variable and then append to it in a loop:
 
 	// Filter returns a new slice holding only
-	// the elements of s that satisfy f()
+	// the elements of s that satisfy fn()
 	func Filter(s []int, fn func(int) bool) []int {
 	    var p []int // == nil
 	    for _, v := range s {