Use http instead of https for the gnu ftp mirror

https seems broken on the Debian image:

START   autotools/hello/42930621-fetch.499.log
START   Fetching https://ftpmirror.gnu.org/gnu/automake/automake-1.16.tar.gz
FAILURE Fetching https://ftpmirror.gnu.org/gnu/automake/automake-1.16.tar.gz
FAILURE tar source at hello.bst [line 16 column 2]: Error mirroring https://ftpmirror.gnu.org/gnu/automake/automake-1.16.tar.gz: <urlopen error [SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:720)>

doc/examples/autotools/project.conf

@@ -10,4 +10,4 @@ element-path: elements
 # Define some aliases for the tarballs we download
 aliases:
   alpine: https://gnome7.codethink.co.uk/tarballs/
-  gnu: https://ftpmirror.gnu.org/gnu/automake/
+  gnu: http://ftpmirror.gnu.org/gnu/automake/