bootstrap.sh: use HTTP-4002.2.19, which supports GHC 7.10

cabal-install/bootstrap.sh

@@ -196,7 +196,7 @@ TRANS_VER="0.4.2.0";   TRANS_VER_REGEXP="0\.[4]\."
                        # >= 0.2.* && < 0.5
 MTL_VER="2.2.1";       MTL_VER_REGEXP="[2]\."
                        #  >= 2.0 && < 3
-HTTP_VER="4000.2.18";  HTTP_VER_REGEXP="4000\.2\.([5-9]|1[0-9]|2[0-9])"
+HTTP_VER="4000.2.19";  HTTP_VER_REGEXP="4000\.2\.([5-9]|1[0-9]|2[0-9])"
                        # >= 4000.2.5 < 4000.3
 ZLIB_VER="0.5.4.2";    ZLIB_VER_REGEXP="0\.[45]\."
                        # == 0.4.* || == 0.5.*