getAuthClient is an instance method

[ofrobots]

Without this fix, I am getting unhandled rejections with the @google-cloud/logging.

❯ node --trace-warnings index.js
[ 0, 4282461 ]
undefined
(node:44617) TypeError: Cannot read property 'config' of undefined
    at Auth.getAuthClient (/Users/ofrobots/tmp/log-t/node_modules/google-gax/node_modules/google-auto-auth/index.js:38:20)
    at /Users/ofrobots/tmp/log-t/node_modules/google-gax/lib/grpc.js:90:5
    at GrpcClient._getCredentials (/Users/ofrobots/tmp/log-t/node_modules/google-gax/lib/grpc.js:89:10)
    at GrpcClient.createStub (/Users/ofrobots/tmp/log-t/node_modules/google-gax/lib/grpc.js:172:15)
    at new LoggingServiceV2Client (/Users/ofrobots/tmp/log-t/node_modules/@google-cloud/logging/src/v2/logging_service_v2_client.js:122:38)
    at Object.LoggingServiceV2ClientBuilder.loggingServiceV2Client (/Users/ofrobots/tmp/log-t/node_modules/@google-cloud/logging/src/v2/logging_service_v2_client.js:832:12)
    at /Users/ofrobots/tmp/log-t/node_modules/@google-cloud/logging/src/index.js:603:52
    at Immediate.<anonymous> (/Users/ofrobots/tmp/log-t/node_modules/google-auto-auth/index.js:146:7)
    at runCallback (timers.js:672:20)
    at tryOnImmediate (timers.js:645:5)

Details

'use strict'

var gcl = require('@google-cloud/logging')();

var gclog = gcl.log('syslog-benchmark');


var t = process.hrtime();
var max = 2;
for (var i = 0; i < max; ++i) {
  gclog.info('hello world');
}

t = process.hrtime(t);
console.log(t);

[codecov-io]

Codecov Report

Merging #132 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #132   +/-   ##
=======================================
  Coverage   92.71%   92.71%           
=======================================
  Files          11       11           
  Lines        1304     1304           
  Branches      269      269           
=======================================
  Hits         1209     1209           
  Misses         95       95

Impacted Files	Coverage Δ
lib/grpc.js	78.57% <100%> (ø)	⬆️

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