Update example_simple_sa.py (#308)

Fixed nonexistent call: await conn.commit()

examples/example_simple_sa.py

@@ -30,7 +30,7 @@ async def go(loop):
         async for row in conn.execute(tbl.select()):
             print(row.id, row.val)
 
-        await conn.commit()
+        await conn.execute("commit")
 
     engine.close()
     await engine.wait_closed()