gnu: password-store: Fix compatibility with GnuPG 2.1.19.

* gnu/packages/patches/password-store-gnupg-compat.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/password-utils.scm (password-store)[source]: Use it.

Signed-off-by: Clément Lassieur <clement@lassieur.org>