updated some examples from ch. 17 e 18 to Python 3.7

Author: ramalho

…futures-py3.7/countries/flags_asyncio.py …futures-py3.7/countries/asyncio_flags.py17-futures-py3.7/countries/flags_asyncio.py renamed to 17-futures-py3.7/countries/asyncio_flags.py 17-futures-py3.7/countries/flags_asyncio.py renamed to 17-futures-py3.7/countries/asyncio_flags.py

@@ -31,17 +31,15 @@ async def slow_function():  # <5>
 
 
 async def supervisor():  # <7>
-    spinner = asyncio.ensure_future(spin('thinking!'))  # <8>
+    spinner = asyncio.create_task(spin('thinking!'))  # <8>
     print('spinner object:', spinner)  # <9>
     result = await slow_function()  # <10>
     spinner.cancel()  # <11>
     return result
 
 
 def main():
-    loop = asyncio.get_event_loop()  # <12>
-    result = loop.run_until_complete(supervisor())  # <13>
-    loop.close()
+    result = asyncio.run(supervisor())  # <12>
     print('Answer:', result)