Use valid celery version

Author: johannalberts

requirements/edx/base.txt

@@ -32,7 +32,7 @@ boto3==1.4.8              # via -r requirements/edx/base.in, fs-s3fs
 boto==2.39.0              # via -r requirements/edx/base.in, django-ses, edxval, ora2
 botocore==1.8.17          # via -r requirements/edx/base.in, boto3, s3transfer
 bridgekeeper==0.9         # via -r requirements/edx/base.in
-celery==3.1.26            # via -c requirements/edx/../constraints.txt, -r requirements/edx/base.in, django-celery, django-user-tasks, edx-celeryutils, edx-enterprise
+celery==3.1.25            # via -c requirements/edx/../constraints.txt, -r requirements/edx/base.in, django-celery, django-user-tasks, edx-celeryutils, edx-enterprise
 certifi==2020.6.20        # via -r requirements/edx/paver.txt, requests
 cffi==1.14.0              # via -r requirements/edx/../edx-sandbox/shared.txt, cryptography
 chardet==3.0.4            # via -r requirements/edx/paver.txt, pdfminer.six, pysrt, requests