singleflight: fix typo in singleflight_test.go

Change-Id: Ia2160fdc8f1938d784a4e1595151c00bc521f5c3
Reviewed-on: https://go-review.googlesource.com/c/sync/+/626795
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Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
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Auto-Submit: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

singleflight/singleflight_test.go

@@ -411,7 +411,7 @@ func ExampleGroup() {
 	// Results are shared by functions executed with duplicate keys.
 	fmt.Println("Shared:", res2.Shared)
 	// Only the first function is executed: it is registered and started with "key",
-	// and doesn't complete before the second funtion is registered with a duplicate key.
+	// and doesn't complete before the second function is registered with a duplicate key.
 	fmt.Println("Equal results:", res1.Val.(string) == res2.Val.(string))
 	fmt.Println("Result:", res1.Val)