runtime/pprof: fix doc typo

Change-Id: I6e814182d89c3e7ff184141af097af0afb844d00
Reviewed-on: https://go-review.googlesource.com/78620Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/pprof/pprof.go

@@ -18,7 +18,7 @@
 // To add equivalent profiling support to a standalone program, add
 // code like the following to your main function:
 //
-//    var cpuprofile = flag.String("cpuprofile", "", "write cpu profile `file`")
+//    var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to `file`")
 //    var memprofile = flag.String("memprofile", "", "write memory profile to `file`")
 //
 //    func main() {