CI: Accept line breaks before binary operators

Quote from PEP8:
 # No: operators sit far away from their operands
 income = (gross_wages +
           taxable_interest +
           (dividends - qualified_dividends) -
           ira_deduction -
           student_loan_interest)

 # Yes: easy to match operators with operands
 income = (gross_wages
           + taxable_interest
           + (dividends - qualified_dividends)
           - ira_deduction
           - student_loan_interest)

ci/compare-pep8.sh

@@ -2,4 +2,4 @@
 set -o nounset -o xtrace -o errexit
 source "$(dirname "$(readlink -f "$0")")/common.sh"
 
-git diff "${MERGEBASE}..${HEAD}" | pep8 --diff --show-source --max-line-length=100 && echo "OK, no PEP8 errors detected"
+git diff "${MERGEBASE}..${HEAD}" | pep8 --ignore=W503 --diff --show-source --max-line-length=100 && echo "OK, no PEP8 errors detected"