Vision: Add 'gccl' header.

[landrito]

Updates #2225

[stephenplusplus]

LGTM - would you mind adding a test? Here's the one from Language: https://github.com/GoogleCloudPlatform/google-cloud-node/blob/03e6373a8edf137b22f01d24f7602964cf530d8f/packages/language/test/index.js#L115

[landrito]

Will do!

[stephenplusplus]

One of the tests wasn't happy:

  1) Vision instantiation should create a gax api client:

      AssertionError: { projectId: 'project-id',
  libName: 'gccl',
  libVersion: '0.11.1' } === { projectId: 'project-id' }
      + expected - actual

       {
      -  "libName": "gccl"
      -  "libVersion": "0.11.1"
         "projectId": "project-id"
       }
      
      at Object.imageAnnotatorClient (test/index.js:117:20)
      at new Vision (src/index.js:69:25)
      at Context.<anonymous> (test/index.js:123:20)

https://circleci.com/gh/GoogleCloudPlatform/google-cloud-node/812?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

[landrito]

Fixed.

[coveralls]

Coverage remained the same at 100.0% when pulling 70970b9 on landrito:vision into 1d1f491 on GoogleCloudPlatform:master.