fix makefile typo

Author: sharifelgamal

Makefile

@@ -14,8 +14,8 @@
 
 # Bump these on release - and please check ISO_VERSION for correctness.
 VERSION_MAJOR ?= 1
-VERSION_MINOR ?= 20
-VERSION_BUILD ?= 1-beta.0
+VERSION_MINOR ?= 21
+VERSION_BUILD ?= 0-beta.0
 RAW_VERSION=$(VERSION_MAJOR).$(VERSION_MINOR).$(VERSION_BUILD)
 VERSION ?= v$(RAW_VERSION)