Fix linter

7 jobs for Cumulant in 16 minutes and 28 seconds (queued for 4 seconds)
Name Stage Failure
failed
ubuntu Test
lbmpy/methods/centeredcumulant/cumulant_transform.py:30: TypeError
============================= 86 tests deselected ==============================
====== 5 failed, 373 passed, 14 skipped, 86 deselected in 667.14 seconds =======
Uploading artifacts for failed job
Uploading artifacts...
report.xml: found 1 matching files and directories

Uploading artifacts as "junit" to coordinator... ok
id=528497 responseStatus=201 Created token=xnAzBMs3
Cleaning up file based variables
ERROR: Job failed: exit code 1