uasyncio.core: Follow builtin "time" module rename to "utime".

Author: Paul Sokolovsky

uasyncio.core/uasyncio/core.py

@@ -1,4 +1,7 @@
-import time
+try:
+    import utime as time
+except ImportError:
+    import time
 import uheapq as heapq
 import logging