finance/py-mplfinance: Update to 0.12.8b6

Changes:	https://github.com/matplotlib/mplfinance/releases

finance/py-mplfinance/Makefile

 # Created by: Po-Chuan Hsieh <sunpoet@FreeBSD.org>
 
 PORTNAME=	mplfinance
-PORTVERSION=	0.12.7a17
+PORTVERSION=	0.12.8b6
 CATEGORIES=	finance python
 MASTER_SITES=	CHEESESHOP
 PKGNAMEPREFIX=	${PYTHON_PKGNAMEPREFIX}

finance/py-mplfinance/distinfo

-TIMESTAMP = 1620928533
-SHA256 (mplfinance-0.12.7a17.tar.gz) = 0331fb99ca10fe59e8870c477603ef21365f8975f0d7288701a32c02d010db24
-SIZE (mplfinance-0.12.7a17.tar.gz) = 59401
+TIMESTAMP = 1643971104
+SHA256 (mplfinance-0.12.8b6.tar.gz) = 78ca3bca1222f631f48b0bd775c62f90f87688aa338af93ff498d9f5003c0bbf
+SIZE (mplfinance-0.12.8b6.tar.gz) = 60666