Custom client on Mutations

[GuteFCO]

Added the possibility to define a custom client in mutations, based on Query component

Checklist:

• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests
• If this was a change that affects the external API used in GitHunt-React, update GitHunt-React and post a link to the PR in the discussion.

[apollo-cla]

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[samyhrer]

Great PR! But to consolidate the API surface, this feature should maybe be added to the Query and Subscription component as well?

[hwillson]

This was already implemented in #1890 and released in react-apollo 2.1.6. Thanks for submitting this PR though!

[samyhrer]

@hwillson Do you know if there are plans to do this for the Subscription-component as well? Or will you accept a PR for that functionality?

[hwillson]

@samyhrer I'd love a PR that adds that functionality!

[hwillson]

@samyhrer Actually, maybe hold off on that PR. I just noticed #1956 implements this across the board. Thanks though!