Remove version lower bound check (#423)

The engines field in package.json serves this purpose now.

PR-URL: #423

index.js

@@ -26,7 +26,6 @@ var common = require('@google-cloud/common');
 var extend = require('extend');
 var constants = require('./src/constants.js');
 var gcpMetadata = require('gcp-metadata');
-var semver = require('semver');
 var traceUtil = require('./src/util.js');
 var TraceApi = require('./src/trace-api.js');
 var pluginLoader = require('./src/trace-plugin-loader.js');
@@ -92,11 +91,6 @@ function start(projectConfig) {
     tag: '@google/cloud-trace'
   });
 
-  if (!semver.satisfies(process.versions.node, '>=0.12')) {
-    logger.error('Tracing is only supported on Node versions >=0.12');
-    return traceApi;
-  }
-
   if (config.projectId) {
     logger.info('Locally provided ProjectId: ' + config.projectId);
   }