makefile: change build order

Move docs to the end of list - build errors in core code can be spotted
earlier.

Makefile.builder

@@ -1,3 +1,3 @@
 ifeq ($(PACKAGE_SET),dom0)
-RPM_SPEC_FILES := $(addprefix rpm_spec/,core-dom0-doc.spec core-dom0.spec)
+RPM_SPEC_FILES := $(addprefix rpm_spec/,core-dom0.spec core-dom0-doc.spec)
 endif