[damned-lies] Fix diff function under Python3

[Claude Paroz <claudep src gnome org>]

commit 5f5a7096bb417a4aba37e8de9a4120cc5298a197
Author: Claude Paroz <claude 2xlibre net>
Date:   Wed Feb 22 12:05:38 2017 +0100

    Fix diff function under Python3
    
    Note that this commit starts dropping Python 2 support.

 stats/potdiff.py |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/stats/potdiff.py b/stats/potdiff.py
index fe37444..7fa0d1e 100644
--- a/stats/potdiff.py
+++ b/stats/potdiff.py
@@ -24,14 +24,14 @@ from __future__ import unicode_literals
 USE_DIFFLIB = 0
 
 def diff(pota, potb):
-    """Returns a list of differing lines between two files."""
+    """Returns a list of differing lines between two text files."""
     with open(pota, "r") as f1:
-        data1 = f1.read().decode('utf-8')
+        data1 = f1.read()
     res1 = _parse_contents(data1)
     res1.sort()
 
     with open(potb, "r") as f2:
-        data2 = f2.read().decode('utf-8')
+        data2 = f2.read()
     res2 = _parse_contents(data2)
     res2.sort()