content: clarify slices code example

Giving the slice a slightly more descriptive name makes
the formatted string in the loop a bit less cryptic.

Change-Id: Idd17014d7528f133c747df080c59a440c533eb0f
Reviewed-on: https://go-review.googlesource.com/19402
Reviewed-by: Andrew Gerrand <adg@golang.org>

content/moretypes.article

diff --git a/content/moretypes.article b/content/moretypes.article
index 8a203aa..904a578 100644
--- a/content/moretypes.article
+++ b/content/moretypes.article
@@ -83,7 +83,7 @@
 
 `[]T` is a slice with elements of type `T`.
 
-`len(s)` returns the length of slice `s`.
+`len(primes)` returns the length of slice `primes`.
 
 .play moretypes/slices.go
 

content/moretypes/slices.go

diff --git a/content/moretypes/slices.go b/content/moretypes/slices.go
index 62b89d7..385283c 100644
--- a/content/moretypes/slices.go
+++ b/content/moretypes/slices.go
@@ -5,10 +5,10 @@
 import "fmt"
 
 func main() {
-	s := []int{2, 3, 5, 7, 11, 13}
-	fmt.Println("s ==", s)
+	primes := []int{2, 3, 5, 7, 11, 13}
+	fmt.Println("primes ==", primes)
 
-	for i := 0; i < len(s); i++ {
-		fmt.Printf("s[%d] == %d\n", i, s[i])
+	for i := 0; i < len(primes); i++ {
+		fmt.Printf("primes[%d] == %d\n", i, primes[i])
 	}
 }