fix(docs-infra): fix the layout of the "Features" page in IE11 (#41183)

IE11 does not support `justify-content: space-evenly` and therefore
falls back to the default (`flex-start`), breaking the layout of the
items in the "Features" page (see the image below).

This commit fixes the layout by specifying `space-around` as a fallback
for `justify-content`, which keeps the layout closer to the intended.

Before: ![features page layout in IE11 before][1]
After: ![features page layout in IE11 after][2]

[1]: https://user-images.githubusercontent.com/8604205/110811038-045bee80-828f-11eb-8027-d5851762a5eb.png
[2]: https://user-images.githubusercontent.com/8604205/110811076-0a51cf80-828f-11eb-98a0-2f2928128dd0.png

PR Close #41183

aio/src/styles/2-modules/_features.scss

@@ -22,6 +22,8 @@
   .feature-row {
     display: flex;
     flex-wrap: wrap;
+    justify-content: space-around;  // This is required for browsers that do not support
+                                    // `space-evenly` (such as IE11).
     justify-content: space-evenly;
 
     @media (max-width: 1057px) {