allow utf-8 encoded characters (#581)

can/dbc.py

@@ -20,7 +20,7 @@ DBCSignal = namedtuple("DBCSignal", ["name", "start_bit", "msb", "lsb", "size",
 class dbc():
   def __init__(self, fn):
     self.name, _ = os.path.splitext(os.path.basename(fn))
-    with open(fn, encoding="ascii") as f:
+    with open(fn, encoding="utf-8") as f:
       self.txt = f.readlines()
     self._warned_addresses = set()