devel/py-astroid: Update to 2.5.6

Changes:	https://github.com/PyCQA/astroid/releases
		https://github.com/PyCQA/astroid/blob/master/ChangeLog

devel/py-astroid/Makefile

 PORTNAME=	astroid
-PORTVERSION=	2.5.4
+PORTVERSION=	2.5.6
 CATEGORIES=	devel python
 MASTER_SITES=	CHEESESHOP
 PKGNAMEPREFIX=	${PYTHON_PKGNAMEPREFIX}

devel/py-astroid/distinfo

-TIMESTAMP = 1619569451
-SHA256 (astroid-2.5.4.tar.gz) = f9f472d4002d55199b1c151ef0570cf71d42aaa34aaa3d29c3e41c75f6f47564
-SIZE (astroid-2.5.4.tar.gz) = 181499
+TIMESTAMP = 1619725343
+SHA256 (astroid-2.5.6.tar.gz) = 8a398dfce302c13f14bab13e2b14fe385d32b73f4e4853b9bdfb64598baa1975
+SIZE (astroid-2.5.6.tar.gz) = 181541