move to rc 0.4.0b6

nxtomomill/version.py

@@ -76,10 +76,10 @@ RELEASE_LEVEL_VALUE = {
 }
 
 MAJOR = 0
-MINOR = 5
+MINOR = 4
 MICRO = 0
 RELEV = "rc"  # <16
-SERIAL = 5  # <16
+SERIAL = 6  # <16
 
 date = __date__