Remove trailing whitespace in generated config

[WhyNotHugo]

pyup-bot creates a PR with a sample config which includes trailing
whitespace.

On repositories that have CI checks for trailing whitespaces, the
default config fails these checks.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.24%. Comparing base (17c2384) to head (c649b16).

Additional details and impacted files

@@ Coverage Diff @@## master #405 +/- ##
=======================================
Coverage 94.24% 94.24% =======================================
Files 11 11 Lines 1164 1164 =======================================
Hits 1097 1097 Misses 67 67 

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.