(setup) fix install crash on non-utf8 systems (#644)

fixes #643

Author: ebr

setup.py

@@ -11,15 +11,15 @@
 defined_macros["CYTHON_CLINE_IN_TRACEBACK"] = 0
 
 # Getting description:
-with open("README.rst") as readme_file:
+with open("README.rst", encoding="utf-8") as readme_file:
     description = readme_file.read()
 
 # Getting requirements:
-with open("requirements.txt") as requirements_file:
+with open("requirements.txt", encoding="utf-8") as requirements_file:
     requirements = requirements_file.readlines()
 
 # Getting version:
-with open("src/dependency_injector/__init__.py") as init_file:
+with open("src/dependency_injector/__init__.py", encoding="utf-8") as init_file:
     version = re.search("__version__ = \"(.*?)\"", init_file.read()).group(1)
 
 # Adding debug options: