use process.version to skip ES6 tests

[0.12 docs](https://nodejs.org/docs/latest-v0.12.x/api/process.html#process_process_version) say

> # Process
> The process object is a global object and can be accessed from anywhere.
>
> ## process.version
> A compiled-in property that exposes NODE_VERSION.

[Current docs](https://nodejs.org/api/process.html#process_process_version) say

> # Process
> The process object is a global that provides information about, and
> control over, the current Node.js process. As a global, it is always
> available to Node.js applications without using require().
>
> ## process.version
> Added in: v0.1.3
> * `<string>`
> The process.version property returns the Node.js version string.

Author: mikesamuel

test/unit/test-Lexer.js

@@ -1,8 +1,5 @@
-var process   = require('process');
-
 // If we're on a Node runtime that should support ES6, run the ES6 tests.
-var nodeVersion = process.env.npm_config_node_version;
-if (/^[0-5][.]/.test(nodeVersion || '')) {
+if (/^v?[0-5][.]/.test(process.version)) {
   // The major version is a single digit in [0, 5].
   console.info('Skipping ES6 tests for node_version %s', nodeVersion);
 } else {

test/unit/test-Template.js

@@ -1,11 +1,9 @@
 var assert    = require('assert');
 var SqlString = require('../../');
-var process   = require('process');
 var test      = require('utest');
 
 // If we're on a Node runtime that should support ES6, run the ES6 tests.
-var nodeVersion = process.env.npm_config_node_version;
-if (/^[0-5][.]/.test(nodeVersion || '')) {
+if (/^v?[0-5][.]/.test(process.version)) {
   // The major version is a single digit in [0, 5].
   console.info('Skipping ES6 tests for node_version %s', nodeVersion);
 } else {