Wrong thumbnail for social media sharing on all landing pages

[brikis98]

When you share the landing pages on social media, they are all using the "Your entire infrastructure. Defined as code. In about a day." purple image from the gruntwork.io main website. This is because all the pages are reusing the header from the main website, which hard-codes the twitter:image and og:image meta tags to this image. We should have different images for each page.