Fix for python3.5 compatibility

rpg/core.py

@@ -219,7 +219,7 @@ def next_read(file, offset_start, offset_end):
     :type offset_end: int
     """
     # Is it a GZIP file?
-    test_file = open(file, "rb")
+    test_file = open(str(file), "rb")
     # Get the first values
     magic = test_file.read(2)
     # Close the file