net/http: soften wording around when the Transport reuses connections

The docs were too specific. Make it vaguer. There are conditions for
which the Transport will try to reuse a connection anyway, even if the
Response Body isn't read to EOF or closed, but we don't need to get
into all the details in the docs.

Fixes #22954

Change-Id: I3b8ae32aeb1a61b396d0026e129552afbfecceec
Reviewed-on: https://go-review.googlesource.com/86276Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/http/response.go

@@ -57,10 +57,9 @@ type Response struct {
 	// The http Client and Transport guarantee that Body is always
 	// non-nil, even on responses without a body or responses with
 	// a zero-length body. It is the caller's responsibility to
-	// close Body. The default HTTP client's Transport does not
-	// attempt to reuse HTTP/1.0 or HTTP/1.1 TCP connections
-	// ("keep-alive") unless the Body is read to completion and is
-	// closed.
+	// close Body. The default HTTP client's Transport may not
+	// reuse HTTP/1.x "keep-alive" TCP connections if the Body is
+	// not read to completion and closed.
 	//
 	// The Body is automatically dechunked if the server replied
 	// with a "chunked" Transfer-Encoding.