chore:tried fixing flake8 errors

src/meanvariancefunction.py

+"""Calculates mean and the variance for a given gene accross all cells."""
+
 import csv
 from glob import glob
 import io
@@ -21,6 +23,7 @@ def mean_variance(filepath: str, output_dir: str = os.getcwd()+'/') -> str:
 
     Raises:
         ValueError: If there are no files in directory
+
     """
     # Open each file in the input directory, raises error if no file is found
     files = [file for file in glob(filepath)]