Remove Python 3.6; add Python 3.10.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zulip/README.md

@@ -3,7 +3,7 @@
 The [Zulip API](https://zulip.com/api) Python bindings require the
 following dependencies:
 
-* **Python (version >= 3.6)**
+* **Python (version >= 3.7)**
 * requests (version >= 0.12.1)
 
 **Note**: If you'd like to use the Zulip bindings with Python 2, we

zulip/integrations/bridge_with_matrix/test_matrix.py

@@ -41,7 +41,7 @@ topic = matrix
 ZULIP_MESSAGE_TEMPLATE: str = "**{username}** [{uid}]: {message}"
 
 
-# For Python 3.6 compatibility.
+# For Python 3.7 compatibility.
 # (Since 3.8, there is unittest.IsolatedAsyncioTestCase!)
 # source: https://stackoverflow.com/a/46324983
 def async_test(coro: Callable[..., Awaitable[Any]]) -> Callable[..., Any]:

zulip/setup.py

@@ -42,12 +42,12 @@ setup(
         "License :: OSI Approved :: Apache Software License",
         "Topic :: Communications :: Chat",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
     ],
-    python_requires=">=3.6",
+    python_requires=">=3.7",
     url="https://www.zulip.org/",
     project_urls={
         "Source": "https://github.com/zulip/python-zulip-api/",