Enforce utf-8 for reading the readme

Fixes failing installation issue #66

Author: nat-n

setup.py

@@ -4,7 +4,7 @@
     name="betterproto",
     version="1.2.3",
     description="A better Protobuf / gRPC generator & library",
-    long_description=open("README.md", "r").read(),
+    long_description=open("README.md", "r", encoding="utf-8").read(),
     long_description_content_type="text/markdown",
     url="http://github.com/danielgtaylor/python-betterproto",
     author="Daniel G. Taylor",