Fix for GTK errors on headless machines

monthplot.py

@@ -1,6 +1,12 @@
 import os, io, subprocess
 import pandas as pd
 import csv, time
+
+if os.environ.get('DISPLAY') is None: # this variable will not be set when X Server is not running
+ import matplotlib as  mplib
+ # set a  different display back-end to squash the error
+ mplib.use('Agg')
+
 import matplotlib.pyplot as plt
 import seaborn as sns