Upgrade psutil to work with newer linux kernels (#820)

The 4.18 kernel introduced a number of new fields into the disk io stats
proc fileystem, and running tests on new versions of linux is causing
failures because psutil cannot interpret the new fields. This fix
updates the version such that it works w/ newer kernels.

Relates giampaolo/psutil#1354

setup.py

@@ -48,7 +48,7 @@ def str_from_file(name):
     # transitive dependency urllib3: MIT
     "elasticsearch==7.0.5",
     # License: BSD
-    "psutil==5.4.0",
+    "psutil==5.6.5",
     # License: MIT
     "py-cpuinfo==3.2.0",
     # License: MIT