bpo-34335: Use async/await syntax in documentation examples (GH-8674)

(cherry picked from commit d2ac400267940f35d731d66c2dafafe099d770d9)

Co-authored-by: Mikhail Terekhov <termim@gmail.com>
diff --git a/Doc/library/asyncio-subprocess.rst b/Doc/library/asyncio-subprocess.rst
index 280b764..60e1745 100644
--- a/Doc/library/asyncio-subprocess.rst
+++ b/Doc/library/asyncio-subprocess.rst
@@ -392,8 +392,7 @@
     import asyncio.subprocess
     import sys
 
-    @asyncio.coroutine
-    def get_date():
+    async def get_date():
         code = 'import datetime; print(datetime.datetime.now())'
 
         # Create the subprocess, redirect the standard output into a pipe