Makefile.defs: version set to 4.2.0-dev6

Makefile.defs

@@ -165,7 +165,7 @@ INSTALL_FLAVOUR=$(FLAVOUR)
 VERSION = 4
 PATCHLEVEL = 2
 SUBLEVEL =  0
-EXTRAVERSION = -dev5
+EXTRAVERSION = -dev6
 
 # memory manager switcher
 # 0 - f_malloc (fast malloc)