Write GitHub the standard way

[wilder]

As we can see in their logo and at the places they write 'GitHub' we can notice that the 'h' is capitalized. This PR changes all the text occurrences were "GitHub" was written as "Github".

[thelinuxfoundation]

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[wilder]

@thelinuxfoundation Signed!

[carl-mastrangelo]

@wilder Merged, Thanks!