net/http, net/http/httputil: start with capitals in deprecation sentences

Fixes #15139

Change-Id: I73111137907e612af871b77ccf166572bf78c840
Reviewed-on: https://go-review.googlesource.com/21544Reviewed-by: Andrew Gerrand <adg@golang.org>

src/net/http/httputil/persist.go

@@ -28,7 +28,7 @@ var errClosed = errors.New("i/o operation on closed connection")
 // Is is low-level, old, and unused by Go's current HTTP stack.
 // We should have deleted it before Go 1.
 //
-// Deprecated: use the Server in package net/http instead.
+// Deprecated: Use the Server in package net/http instead.
 type ServerConn struct {
 	mu              sync.Mutex // read-write protects the following fields
 	c               net.Conn
@@ -45,7 +45,7 @@ type ServerConn struct {
 // Is is low-level, old, and unused by Go's current HTTP stack.
 // We should have deleted it before Go 1.
 //
-// Deprecated: use the Server in package net/http instead.
+// Deprecated: Use the Server in package net/http instead.
 func NewServerConn(c net.Conn, r *bufio.Reader) *ServerConn {
 	if r == nil {
 		r = bufio.NewReader(c)
@@ -221,7 +221,7 @@ func (sc *ServerConn) Write(req *http.Request, resp *http.Response) error {
 // Is is low-level, old, and unused by Go's current HTTP stack.
 // We should have deleted it before Go 1.
 //
-// Deprecated: use Client or Transport in package net/http instead.
+// Deprecated: Use Client or Transport in package net/http instead.
 type ClientConn struct {
 	mu              sync.Mutex // read-write protects the following fields
 	c               net.Conn
@@ -239,7 +239,7 @@ type ClientConn struct {
 // Is is low-level, old, and unused by Go's current HTTP stack.
 // We should have deleted it before Go 1.
 //
-// Deprecated: use the Client or Transport in package net/http instead.
+// Deprecated: Use the Client or Transport in package net/http instead.
 func NewClientConn(c net.Conn, r *bufio.Reader) *ClientConn {
 	if r == nil {
 		r = bufio.NewReader(c)
@@ -256,7 +256,7 @@ func NewClientConn(c net.Conn, r *bufio.Reader) *ClientConn {
 // Is is low-level, old, and unused by Go's current HTTP stack.
 // We should have deleted it before Go 1.
 //
-// Deprecated: use the Client or Transport in package net/http instead.
+// Deprecated: Use the Client or Transport in package net/http instead.
 func NewProxyClientConn(c net.Conn, r *bufio.Reader) *ClientConn {
 	cc := NewClientConn(c, r)
 	cc.writeReq = (*http.Request).WriteProxy

src/net/http/request.go

@@ -249,7 +249,7 @@ type Request struct {
 	//
 	// For server requests, this field is not applicable.
 	//
-	// Deprecated: use the Context and WithContext methods
+	// Deprecated: Use the Context and WithContext methods
 	// instead. If a Request's Cancel field and context are both
 	// set, it is undefined whether Cancel is respected.
 	Cancel <-chan struct{}