tour: use same name in code and explanation

Fixes golang/go#11713

Change-Id: If7e28520635ca1edf9c1e93f431163a8473201b1
Reviewed-on: https://go-review.googlesource.com/12200
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/content/concurrency/buffered-channels.go b/content/concurrency/buffered-channels.go
index 21748dd..b5abf10 100644
--- a/content/concurrency/buffered-channels.go
+++ b/content/concurrency/buffered-channels.go
@@ -5,9 +5,9 @@
 import "fmt"
 
 func main() {
-	c := make(chan int, 2)
-	c <- 1
-	c <- 2
-	fmt.Println(<-c)
-	fmt.Println(<-c)
+	ch := make(chan int, 2)
+	ch <- 1
+	ch <- 2
+	fmt.Println(<-ch)
+	fmt.Println(<-ch)
 }