Remove "coding: utf-8" source declarations

Now that we only support Python 3, we know that the encoding of source
files is UTF-8 by default: https://www.python.org/dev/peps/pep-3120/.

Author: bbc2

setup.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 import io
 from setuptools import setup
 

src/dotenv/main.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 from __future__ import absolute_import, print_function, unicode_literals
 
 import io

tests/test_cli.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 import os
 
 import pytest

tests/test_main.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
 import io

tests/test_parser.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 import io
 
 import pytest