Fix mutation error action before reject ApolloError

[cncolder]

• If this PR is a new feature, 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
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass
• Update CHANGELOG.md with your change
• Add your name and email to the AUTHORS file (optional)
• If this was a change that affects the external API, update the docs and post a link to the PR in the discussion

This patch fix issue #1386

[apollo-cla]

@cncolder: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[helfer]

@cncolder Thanks for the PR! Please also add a test that fails without this code change! It could go in the test/client.ts file. You can simply check if the store still contains the optimistic update after the server (mockNetworkInterface) sent back a response with GraphQL errors.

[cncolder]

test added

[helfer]

Looks good now, thanks a lot @cncolder ! 🙂