Migrate from os.rename to shutil.move

`os.rename` is brittle and prone to failure. Among other things, it struggles with moving files between mount points. Something that's required if you have docker volumes. Should also address dbr#154

tvnamer/utils.py

@@ -1006,7 +1006,7 @@ def delete_file(fpath):
 def rename_file(old, new):
     p("rename %s to %s" % (old, new))
     stat = os.stat(old)
-    os.rename(old, new)
+    shutil.move(old, new)
     try:
         os.utime(new, (stat.st_atime, stat.st_mtime))
     except OSError as ex: