Take ledger-default-date-format in to account for sorting

[MikiDi]

SPC m C (ledger-mode-clean-buffer) doesn't sort as expected in case of a non-alphabetically sorting date format.
Configuring my default date format doesn't change anything to this.

(defun dotspacemacs/user-config ()
  "Configuration for user code:
This function is called at the very end of Spacemacs startup, after layer
configuration.
Put your configuration code here, except for variables that should be set
before packages are loaded."
  (setq ledger-default-date-format "%d/%m/%Y")
  (setq ledger-init-file-name "/home/michael/.ledgerrc")
)

This might be due to ledger/ledger#1068 , but then the wording sort chronologically in ledger-mode sources is at least a little misleading.