remove extraneous CRLF after message-body

RFC2616 section 4.1 (http://www.ietf.org/rfc/rfc2616.txt):
"... an HTTP/1.1 client MUST NOT preface or follow a request
with an extra CRLF."
(cherry picked from commit d0e8e715b4)

racket/collects/net/http-client.rkt

@@ -128,8 +128,7 @@
     (fprintf to "~a\r\n" h))
   (fprintf to "\r\n")
   (when data
-    (display data to)
-    (fprintf to "\r\n"))
+    (display data to))
   (flush-output to))
 
 (define (http-conn-status! hc)