bpo-35283: Update the docstring of threading.Thread.join method (GH-11596)

Lib/threading.py

@@ -1007,7 +1007,7 @@ class Thread:
         When the timeout argument is present and not None, it should be a
         floating point number specifying a timeout for the operation in seconds
         (or fractions thereof). As join() always returns None, you must call
-        isAlive() after join() to decide whether a timeout happened -- if the
+        is_alive() after join() to decide whether a timeout happened -- if the
         thread is still alive, the join() call timed out.
 
         When the timeout argument is not present or None, the operation will