Update request urllib3 (#464)

* requests: updated to version 2.27.1

* urllib3: updated to version 1.26.18

lib/urllib3/contrib/_appengine_environ.py

@@ -6,27 +6,31 @@ import os
 
 
 def is_appengine():
-    return is_local_appengine() or is_prod_appengine() or is_prod_appengine_mvms()
+    return is_local_appengine() or is_prod_appengine()
 
 
 def is_appengine_sandbox():
-    return is_appengine() and not is_prod_appengine_mvms()
+    """Reports if the app is running in the first generation sandbox.
+
+    The second generation runtimes are technically still in a sandbox, but it
+    is much less restrictive, so generally you shouldn't need to check for it.
+    see https://cloud.google.com/appengine/docs/standard/runtimes
+    """
+    return is_appengine() and os.environ["APPENGINE_RUNTIME"] == "python27"
 
 
 def is_local_appengine():
-    return (
-        "APPENGINE_RUNTIME" in os.environ
-        and "Development/" in os.environ["SERVER_SOFTWARE"]
-    )
+    return "APPENGINE_RUNTIME" in os.environ and os.environ.get(
+        "SERVER_SOFTWARE", ""
+    ).startswith("Development/")
 
 
 def is_prod_appengine():
-    return (
-        "APPENGINE_RUNTIME" in os.environ
-        and "Google App Engine/" in os.environ["SERVER_SOFTWARE"]
-        and not is_prod_appengine_mvms()
-    )
+    return "APPENGINE_RUNTIME" in os.environ and os.environ.get(
+        "SERVER_SOFTWARE", ""
+    ).startswith("Google App Engine/")
 
 
 def is_prod_appengine_mvms():
-    return os.environ.get("GAE_VM", False) == "true"
+    """Deprecated."""
+    return False