Update Twitter/FB meta images

[mkiser]

It's a minor enhancement, but it makes sharing the dev center on social look more polished. Three small things:

Replace:

<meta property="og:image" content="https://algorithmia.com/developers/images/logos/AlgorithmiaLogo_fb.png">
With:

And replace:
<meta name="twitter:image" content="https://algorithmia.com/developers/images/logos/AlgorithmiaLogo_tw.png">

with

NOTE: These two images are slightly different aspect ratios -- specific to the platform.

And finally, change:
<meta name="twitter:card" content="summary">
to:
<meta name="twitter:card" content="summary_large_image">

^ this last one will make tweets about the dev center appear like this:

instead of this: