migrate_config: scalloc converted config

migrate_config: scalloc converted config

Prevents a false-positive error eg with config file:
set $mod Mod4
bindsym $mod+h split h
bindsym $mod+v split v

ERROR: CONFIG: Expected one of these tokens: <end>, '#', 'set ', ...
ERROR: CONFIG: Line   8:     status_command i3status
ERROR: CONFIG: Line   9: }
ERROR: CONFIG: Line  10: <BE><BE><BE><BE><BE><BE>