bug: remove six requirement, add license classifer

There are a few other "poetry" related changes
that should be made, but I'm skipping those for
now.

Closes #166, 167

Author: jrconlin

Diff for: pyproject.toml

@@ -24,12 +24,19 @@ classifiers = [
     "Programming Language :: Python :: Implementation :: PyPy",
     "Programming Language :: Python",
     "Programming Language :: Python :: 3",
+    "License :: OSI Approved :: Mozilla Public License 2.0 (MPL 2.0)",
 ]
 # use the following fields defined in the setup.py file
 # (When the guides talk about something being "dynamic", they
 # want you to add the field here.
 dynamic = ["version", "entry-points"]
-dependencies = ['aiohttp', 'cryptography>=2.6.1', 'http-ece>=1.1.0', 'requests>=2.21.0', 'six>=1.15.0', 'py-vapid>=1.7.0']
+dependencies = [
+    'aiohttp',
+    'cryptography>=2.6.1',
+    'http-ece>=1.1.0',
+    'requests>=2.21.0',
+    'py-vapid>=1.7.0',
+]
 
 [project.urls]
 Homepage = "https://github.com/web-push-libs/pywebpush"

Diff for: pywebpush/__init__.py

@@ -19,7 +19,6 @@
 import aiohttp
 import http_ece
 import requests
-import six
 from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives.asymmetric import ec
 from cryptography.hazmat.primitives import serialization
@@ -175,7 +174,7 @@ def __init__(
             for k in ["p256dh", "auth"]:
                 if keys.get(k) is None:
                     raise WebPushException("Missing keys value: {}".format(k))
-                if isinstance(keys[k], six.text_type):
+                if isinstance(keys[k], str):
                     keys[k] = bytes(cast(str, keys[k]).encode("utf8"))
             receiver_raw = base64.urlsafe_b64decode(
                 self._repad(cast(bytes, keys["p256dh"]))
@@ -236,7 +235,7 @@ def encode(
             format=serialization.PublicFormat.UncompressedPoint,
         )
 
-        if isinstance(data, six.text_type):
+        if isinstance(data, str):
             data = bytes(data.encode("utf8"))
         if content_encoding == "aes128gcm":
             self.verb("Encrypting to aes128gcm...")

Diff for: requirements.txt

@@ -2,5 +2,4 @@ aiohttp
 cryptography>=2.6.1
 http-ece>=1.1.0
 requests>=2.21.0
-six>=1.15.0
 py-vapid>=1.7.0

Diff for: setup.py

@@ -9,7 +9,7 @@
 
 from setuptools import find_packages, setup
 
-__version__ = "2.0.0"
+__version__ = "2.1.0"
 
 
 def read_from(file):