statistics/statistics.py: fixed bug in counting

  # for each tree in the inputfile

  for line in f:

    # remove all '}', split line by '{' and remove empty entries at the beginning and end

    nodes = re.split(r'[{]', re.sub('[\}]', '', line))[1:-1]

    nodes = re.split(r'[{]', re.sub('[\}]', '', line.rstrip()))[1:]

    # get tree size

    tree_size = len(nodes)

    # sum to compute average