Bump master branch to 4.5dev

Note that the next release is intended to be 5.0 to coincide with the
release of PostgreSQL 12; 4.5 is currently a placeholder in case we
need to push out a feature release before then.

repmgr.control

@@ -1,6 +1,6 @@
 # repmgr extension
 comment = 'Replication manager for PostgreSQL'
-default_version = '4.4'
+default_version = '4.5'
 module_pathname = '$libdir/repmgr'
 relocatable = false
 schema = repmgr