doc: fix typo in cookie.go

Author: mbj36

src/net/http/cookie.go

@@ -38,7 +38,7 @@ type Cookie struct {
 
 // SameSite allows a server to define a cookie attribute making it impossible for
 // the browser to send this cookie along with cross-site requests. The main
-// goal is to mitigate the risk of cross-origin information leakage, and provides
+// goal is to mitigate the risk of cross-origin information leakage, and provide
 // some protection against cross-site request forgery attacks.
 //
 // See https://tools.ietf.org/html/draft-ietf-httpbis-cookie-same-site-00 for details.