Use time.monotonic on py3.3+

On Python 3.3 or newer, `monotonic` module aliases `time.monotonic`
from the standard library. On older versions, it will fall back to
an equivalent platform specific implementation provided by the
`monotonic` module.
Attempting to import `time.monotonic` right off the bat removes
the need for additional dependency on modern python installations.

fastpurge/_client.py

@@ -7,12 +7,16 @@
 
 import requests
 
+try:
+    from time import monotonic
+except ImportError:  # pragma: no cover
+    from monotonic import monotonic
+
 from six import string_types
 from six.moves.urllib.parse import urljoin
 
 from akamai.edgegrid import EdgeGridAuth
 from akamai.edgegrid.edgerc import EdgeRc
-from monotonic import monotonic
 from more_executors import Executors
 from more_executors.futures import f_sequence
 

requirements.txt

@@ -1,5 +1,5 @@
 requests
 more-executors>=2.7.0
 six
-monotonic
+monotonic; python_version < '3.3'
 edgegrid-python

tests/test_purge.py

@@ -2,7 +2,10 @@
 import requests_mock
 import mock
 
-from monotonic import monotonic
+try:
+    from time import monotonic
+except ImportError:
+    from monotonic import monotonic
 
 from fastpurge import FastPurgeClient, FastPurgeError