Fix overflow of variants in productView/Variants.jsx

[kaysond]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

If a product has too many variants, it overflows the page

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

Use flex-wrap to wrap variants and gap to keep consistent gap between rows and columns

[kaysond]

@treoden - can you please merge this? :)