net/http: fix typo in doc string

Change-Id: I4542f6c095a35a4dec03c67c45a75a155197eb56
Reviewed-on: https://go-review.googlesource.com/74650Reviewed-by: Tom Bergan <tombergan@google.com>

src/net/http/client.go

@@ -760,7 +760,7 @@ func PostForm(url string, data url.Values) (resp *Response, err error) {
 // with data's keys and values URL-encoded as the request body.
 //
 // The Content-Type header is set to application/x-www-form-urlencoded.
-// To set other headers, use NewRequest and DefaultClient.Do.
+// To set other headers, use NewRequest and Client.Do.
 //
 // When err is nil, resp always contains a non-nil resp.Body.
 // Caller should close resp.Body when done reading from it.