Visually centered a few icons, some new paths and optimizations.

Apple - Visually centered and change the path to more a accurate one.
Bytes: 1011 —> 580.

Dropbox - Visually centered and change the path to fix point alignment.
Bytes: 338 —> 350.

Twitter - Visually centered.
Bytes: 425 —> 431.

Ubuntu - Visually centered and change the path and color to a more
accurate one.
Bytes: 755 —> 674.

Vimeo - Visually centered.
Bytes: 375 —> 379.

WhatsApp - Visually centered and change the path and color to more a
accurate one.
Bytes: 646 —> 611.

Windows - Visually centered and change the path to fix the lines
between shapes.
Bytes: 274 —> 284.

Hope this helps.

FYI: Wikicommons have good SVG shapes and most companies have brand
guidelines with accurate logo renditions and colors.

images/svg/twitter.svg

@@ -1 +1,4 @@
-<svg xmlns="http://www.w3.org/2000/svg" aria-label="Twitter" role="img" viewBox="0 0 512 512"><rect width="512" height="512" fill="#1da1f3" rx="15%"/><path fill="#fff" d="M456 133c-14 7-31 11-47 13 17-10 30-27 37-46-15 10-34 16-52 20-61-62-157-7-141 75-68-3-129-35-169-85-22 37-11 86 26 109-13 0-26-4-37-9 0 39 28 72 65 80-12 3-25 4-37 2 10 33 41 57 77 57-42 30-77 38-122 34 170 111 378-32 359-208 16-11 30-25 41-42z"/></svg>
+<svg role="img" aria-label="Twitter" viewBox="0 0 512 512" xmlns="http://www.w3.org/2000/svg">
+<rect fill="#1da1f3" height="512" rx="15%" width="512"/>
+<path d="M465 135c-14 7-31 11-47 13 17-10 30-27 37-46-15 10-34 16-52 20a83 83 0 0 0-141 75c-68-3-129-35-169-85a80 80 0 0 0 26 109c-13 0-26-4-37-9 0 39 28 72 65 80-12 3-25 4-37 2 10 33 41 57 77 57-42 30-77 38-122 34 170 111 378-32 359-208 16-11 30-25 41-42z" fill="#fff"/>
+</svg>