Bump from 5.4-dev-47-g32792dc6 to at least 5.5 to reflect security updates in all versions before 5.5, but to 5.6-dev to show it's in development ahead of released 5.5.

Author: mikebrady

configure.ac

@@ -1,7 +1,7 @@
 # Process this file with autoconf to produce a configure script.
 
 AC_PREREQ([2.50])
-AC_INIT([shairport-sync], [5.4-dev], [4265913+mikebrady@users.noreply.github.com])
+AC_INIT([shairport-sync], [5.6-dev], [4265913+mikebrady@users.noreply.github.com])
 : ${CFLAGS="-O3"}
 : ${CXXFLAGS="-O3"}
 AM_INIT_AUTOMAKE([subdir-objects])