component/defaults.cfg: fix calculation of min_version

with current min_version set in component/defaults.cfg depending on the
order of extend of buildout, sometimes the min_version of components is
not respected.

This should be fixed by using += everywhere but it needs
!1551

component/defaults.cfg

@@ -34,11 +34,8 @@ depends =
 # python requirements for which the compiler does not matter
   ${patch:recipe}
 recipe = slapos.recipe.build
-# Latest version provided by SlapOS.
+# Default version provided by SlapOS.
 part = gcc-10.5
-# Minimum version for all components that might be required for
-# slapos.rebootstrap (see https://bugs.python.org/issue34112 about Python 3.7+).
-min_version = 5.4
 init =
   import os, subprocess
   parse_version = lambda ver: tuple(map(int, ver.strip().split('.')))