change url for new octicons-v2

[ashygee]

updated link to point to url within primer.style domain.

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[colebemis]

primer.style/octicons-v2 points to the icons that in the primer/octicons-v2 which are no longer up-to-date. Here's a diagram that shows the current state of things:

Our two options moving forward are to update the alias primer.style/octicons-v2 to point to the most up-to-date v2 icons or revert this PR. I think updating the alias is probably the better option.

[ashygee]

@colebemis I think that's the better option too. Are you able to do this?