[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

tests/test_custom_mods.py

@@ -2,6 +2,7 @@
 import pyhf.exceptions as exceptions
 import pytest
 
+
 class custom_builder:
     def __init__(self, pdfconfig):
         self.config = pdfconfig
@@ -26,6 +27,7 @@ def append(self, key, channel, sample, thismod, defined_samp):
     def finalize(self):
         return self.builder_data
 
+
 class custom_applicator:
     op_code = 'multiplication'
     name = 'customfunc'