Story Promo - Leading variant needs fallback gutter

[sareh]

Describe the bug
When viewing in IE11 (that doesn't support CSS Grid), we do not have a gutter - 1rem of spacing between the image block and the text block

To Reproduce
Steps to reproduce the behaviour:

1. Go to Storybook example
2. Adjust window so that text fills the whole text block
3. See text touching the image without necessary spacing.

Expected behaviour
To have a 1rem space between the image and text block

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Testing notes

• This bug fix is expected to need manual testing.

Additional context
Add any other context about the problem here.