Update MacPorts Badge (#288)

README.md

@@ -5,7 +5,7 @@
 <a href="https://boltons.readthedocs.io/en/latest/"><img src="https://img.shields.io/badge/docs-latest-brightgreen.svg?style=flat"></a>
 <a href="https://pypi.python.org/pypi/boltons"><img src="https://img.shields.io/pypi/v/boltons.svg"></a>
 <a href="https://anaconda.org/conda-forge/boltons"><img src="https://img.shields.io/conda/vn/conda-forge/boltons.svg"></a>
-<a href="https://ports.macports.org/port/py-boltons/summary"><img src="https://img.shields.io/badge/macports-v20.2.1-blue?logo=Apple&logoColor=white"></a>
+<a href="https://ports.macports.org/port/py-boltons/summary"><img src="https://repology.org/badge/version-for-repo/macports/python:boltons.svg?header=🍎 MacPorts"></a>
 <a href="https://pypi.python.org/pypi/boltons"><img src="https://img.shields.io/pypi/pyversions/boltons.svg"></a>
 <a href="http://calver.org"><img src="https://img.shields.io/badge/calver-YY.MINOR.MICRO-22bfda.svg"></a>