curl: fix idn2 disabling

It's not default enabled to this doesn't have include any behavior change,
however we are now sure that libidn will not be enabled in curl if we were to
start building it

Author: chouquette

config/software/curl.rb

@@ -46,7 +46,7 @@
            "--enable-proxy",
            "--disable-dependency-tracking",
            "--enable-ipv6",
-           "--without-libidn",
+           "--without-libidn2",
            "--without-gnutls",
            "--without-librtmp",
            "--without-libssh2",