[release-branch.go1.12] net/http/httptrace: fix typo

Change-Id: I15279e4aa9306bde925929907a7b5e7ef5d8b642
GitHub-Last-Rev: 6bc2d66aecd424b322ec0c23b280e74cb22e08c3
GitHub-Pull-Request: golang/go#30193
Reviewed-on: https://go-review.googlesource.com/c/162018Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
(cherry picked from commit 1edd2a34)
Reviewed-on: https://go-review.googlesource.com/c/162359Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/http/httptrace/trace.go

@@ -152,7 +152,7 @@ type ClientTrace struct {
 	WroteHeaders func()
 
 	// Wait100Continue is called if the Request specified
-	// "Expected: 100-continue" and the Transport has written the
+	// "Expect: 100-continue" and the Transport has written the
 	// request headers but is waiting for "100 Continue" from the
 	// server before writing the request body.
 	Wait100Continue func()