cmd/go: fix typo in docs

Fixes #5181.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/8277043

src/cmd/go/doc.go

@@ -717,8 +717,9 @@ control the execution of any test:
 	    when all tests are complete.
 
 	-blockprofilerate n
-	    Control the detail provided in goroutine blocking profiles by setting
-	    runtime.BlockProfileRate to n.  See 'godoc runtime BlockProfileRate'.
+	    Control the detail provided in goroutine blocking profiles by
+	    calling runtime.SetBlockProfileRate with n.
+	    See 'godoc runtime SetBlockProfileRate'.
 	    The profiler aims to sample, on average, one blocking event every
 	    n nanoseconds the program spends blocked.  By default,
 	    if -test.blockprofile is set without this flag, all blocking events

src/cmd/go/test.go

@@ -107,8 +107,9 @@ control the execution of any test:
 	    when all tests are complete.
 
 	-blockprofilerate n
-	    Control the detail provided in goroutine blocking profiles by setting
-	    runtime.BlockProfileRate to n.  See 'godoc runtime BlockProfileRate'.
+	    Control the detail provided in goroutine blocking profiles by
+	    calling runtime.SetBlockProfileRate with n.
+	    See 'godoc runtime SetBlockProfileRate'.
 	    The profiler aims to sample, on average, one blocking event every
 	    n nanoseconds the program spends blocked.  By default,
 	    if -test.blockprofile is set without this flag, all blocking events