Tidied some import statements.

tests/test_compare_experimental.py

@@ -16,7 +16,10 @@
 # You should have received a copy of the GNU General Public License
 # along with gprMax.  If not, see <http://www.gnu.org/licenses/>.
 
-import sys, os, argparse
+import argparse
+import os
+import sys
+
 import h5py
 import numpy as np
 import matplotlib.pyplot as plt