Backport of PR-13777. Mobile 'Payments methods' step looks bad on mobile

[Frodigo]

Description

This is the backport of #13777

Fixed Issues (if relevant)

1. Mobile "Payment Methods" step looks bad on mobile #13315: I "Payment Methods" step looks bad on mobile

Manual testing scenarios

1. Go to frontend, add some product to shopping cart on mobile (or in iphone emulation mode on chrome)
2. Go to Checkout, fill "shipping" step, click "Next" button
3. See "Payment Methods" block
4. Step title heading "Payment Method" should be correctly aligned with other elements in this section

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)