Fix get_long_description

`open` use different default encodings on different operating systems

setup.py

@@ -69,7 +69,7 @@ def get_install_requires():
 
 
 def get_long_description():
-    with open("README.md") as f:
+    with open("README.md", "r", encoding="utf-8") as f:
         long_description = f.read()
     try:
         # when this package is being released