Update circleci/node version

[fenglish]

• Update circleci/node version 6 to 8
  because I got the error below when I try to release new version of next-metrics

npx snyk monitor --org=customer-products --project-name=Financial-Times/next-metrics
/bin/bash: npx: command not found

https://circleci.com/gh/Financial-Times/next-metrics/2238

npx is provided from npm version ^5.2.0
The Circle build's npm version is 3.10.10

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• Update mitm version to the latest(1.7.0)
  The npx issue is resolved by node version update but I get a different error related to the update.

  1 failing

  1) Logging to graphite
       Send metrics to Graphite:
     TypeError: normalizeConnectArgs is not a function
      at Mitm.connect (node_modules/mitm/index.js:70:14)
      at Graphite.log (lib/graphite/client.js:6:247)
      at Context.<anonymous> (test/unit/client.spec.old.js:43:5)

https://circleci.com/gh/Financial-Times/next-metrics/2240

mitm needs to be update from1.2.0 to ^1.3.2 to solve the error.

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• Delete not really important part for solving a test failed
  When I updated mitm version, I got a different error with the same test.

  1 failing

  1) Logging to graphite
       Send metrics to Graphite:
     Error: Timeout of 2000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/home/circleci/project/build/test/unit/client.spec.old.js)

https://circleci.com/gh/Financial-Times/next-metrics/2246

Somehow clock in the test causes the error. The test needs to check Logging to graphite. It is not super important to know what exactly is the log at this point. The clock is deleted to solve the issue to able to release new version of next-metrics.

However, the time stamp thing is nice to have so I created #339 for someone has time to tackle to put sinon clock back.

[adambraimbridge]

👍