Fixed broken image in styleguide.md

[buck06191]

Description of the change: Fixed broken image embed in styleguide.md
Reason for the change: Image didn't show. instead there was a broken <src ... /> tag
Link to original source: [styleguide.md] (https://github.com/sendgrid/docs/blob/develop/styleguide.md)

Closes ##4303

[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

Hello @buck06191,

Thanks again for the PR!

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Team SendGrid DX

[thinkingserious]

Hello @buck06191,

Thanks again for the PR!

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Team SendGrid DX

[thinkingserious]

Hello @buck06191,

Thanks again for the PR!

You have earned 1 out of the 5 points needed to receive glorious SendGrid Hacktoberfest swag.

Please take a moment to checkout this link to find more issues to get you past the required threshold or to simply continue the celebration.

Also, please be sure you have officially registered with us here by November 1, 2018 to qualify.

If you have any questions you can email us at dx+hacktoberfest2018@sendgrid.com.

Thank you and Happy Hacktobering!

Team SendGrid