net/http: add missing words to SameSite doc/comments

Change-Id: Ie7f6592d726eba73a5e6b3203e083bff55ff8e4e
GitHub-Last-Rev: 4e317b39dd337f95aa7b7f321906e69a2c14b84e
GitHub-Pull-Request: golang/go#27977
Reviewed-on: https://go-review.googlesource.com/c/139100Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/cookie.go

@@ -36,9 +36,9 @@ type Cookie struct {
 	Unparsed []string // Raw text of unparsed attribute-value pairs
 }
 
-// SameSite allows a server define a cookie attribute making it impossible for
+// 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 mitigate the risk of cross-origin information leakage, and provides
+// goal is to mitigate the risk of cross-origin information leakage, and provides
 // some protection against cross-site request forgery attacks.
 //
 // See https://tools.ietf.org/html/draft-ietf-httpbis-cookie-same-site-00 for details.