Remove monotonic usage

The monotonic package was needed for monotonic time operations when
running under Python runtimes older than 3.3. Since we now only support
versions higher than this, this third party package requirement can now
be removed.

Change-Id: I0e5bf6090ed85db2659b50096122a9abda9dde6a
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

futurist/_utils.py

@@ -19,16 +19,13 @@ import inspect
 import multiprocessing
 import sys
 import threading
+from time import monotonic
 import traceback
 
-try:
-    from monotonic import monotonic as now  # noqa
-except ImportError:
-    import time
-    now = time.monotonic
-
 import six
 
+now = monotonic
+
 try:
     import eventlet as _eventlet  # noqa
     EVENTLET_AVAILABLE = True