Most Read not using grid fallback on IE

[thekp]

Describe the bug
Since this PR has been merged: #3200 most read component has been not using the Grid fallback on IE.

To Reproduce
Steps to reproduce the behaviour:

1. Go to 'https://bbc.github.io/psammead/?path=/story/components-mostread-list--default' on IE browser
2. See error

Expected behaviour
We expect the Grid component fallback css to be applied, and for most read to have the correct number of columns at the correct viewport. At the moment it's just a single column for all viewports.

When multi column is selected, we expect 5 columns at largest viewport (gel group 5), 2 colums from group 3-4 and one column from group 2 and below.

When twoColumn is selected, we expect 2 columns at largest viewport (gel group 5) to group 3 and one column from group 2 and below

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.