dvc: fixes style issues with string ops

dvc/command/diff.py

@@ -41,11 +41,11 @@ def add_parser(subparsers, parent_parser):
         "target", help="Source path to a data file or directory."
     )
     diff_parser.add_argument(
-        "a_ref", help="Git tag/reference from which diff calculates"
+        "a_ref", help="Git reference from which diff calculates"
     )
     diff_parser.add_argument(
         "b_ref",
-        help="Git tag/reference till which diff calculates",
+        help="Git reference till which diff calculates",
         nargs="?",
         default=None,
     )

dvc/repo/diff.py

@@ -1,3 +1,5 @@
+from __future__ import unicode_literals
+
 import os
 import math
 
@@ -21,7 +23,7 @@ def _convert_size(size_bytes):
     i = int(math.floor(math.log(size_bytes, 1024)))
     p = math.pow(1024, i)
     s = round(size_bytes / p, 2)
-    return "%s %s" % (s, size_name[i]), sign
+    return "{} {}".format(s, size_name[i]), sign
 
 
 def _get_tree_changes(self, a_entries, b_entries):