net/http: correct subtle transposition of offset and whence in test

Change-Id: I788972bdf85c0225397c0e74901bf9c33c6d30c7
GitHub-Last-Rev: 57737fe782bf7ad2d765c2efd80d75b3baca2c7b
GitHub-Pull-Request: golang/go#24265
Reviewed-on: https://go-review.googlesource.com/98761Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/fs_test.go

@@ -993,7 +993,7 @@ func TestServeContent(t *testing.T) {
 		for _, method := range []string{"GET", "HEAD"} {
 			//restore content in case it is consumed by previous method
 			if content, ok := content.(*strings.Reader); ok {
-				content.Seek(io.SeekStart, 0)
+				content.Seek(0, io.SeekStart)
 			}
 
 			servec <- serveParam{