Fix appolo-server-micro top level error response

[fromthemills]

Fix for (#1581)

apollo-server-micro does not handle context or schema errors correctly. Instead of just throwing when error is caught the error message should be return as the response body.

TODO:

• Update CHANGELOG.md with your change (include reference to issue & this PR)
• 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

[apollo-cla]

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