allow i686 as a supported architecture

This is checked during preflight. See https://github.com/mail-in-a-box/mailinabox/issues/885 (#889)

setup/preflight.sh

@@ -47,15 +47,15 @@ if [ -e ~/.wgetrc ]; then
 	exit
 fi
 
-# Check that we are running on x86_64, any other architecture is unsupported and
+# Check that we are running on x86_64 or i686, any other architecture is unsupported and
 # will fail later in the setup when we try to install the custom build lucene packages.
 #
 # Set ARM=1 to ignore this check if you have built the packages yourself. If you do this
 # you are on your own!
 ARCHITECTURE=$(uname -m)
-if [ "$ARCHITECTURE" != "x86_64" ]; then
+if [ "$ARCHITECTURE" != "x86_64" ] && [ "$ARCHITECTURE" != "i686" ]; then
 if [ -z "$ARM" ]; then
-	echo "Mail-in-a-Box only supports x86_64 and will not work on any other architecture, like ARM."
+	echo "Mail-in-a-Box only supports x86_64 or i686 and will not work on any other architecture, like ARM."
 	echo "Your architecture is $ARCHITECTURE"
 	exit
 fi