Bail out if not a valid version of node. Fixes gh-764

Sure, this is incredibly brutal, but the usb module DOESN'T WORK on Node.js > 4, so there is no point in being misleading. This is "fail hard, fail early" at its bluntest.

Related to gh-828

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>

bin/tessel-2.js

@@ -19,6 +19,11 @@ const CLI_ENTRYPOINT = 'cli.entrypoint';
 // Check for updates
 const pkg = require('../package.json');
 
+if (parseInt(process.versions.node) !== 4) {
+  log.error('Tessel 2 CLI (t2-cli) is supported for use with the Node.js 4.x.x LTS Release.');
+  process.exit();
+}
+
 /*
  * If a command has been run with root,
  * do not try to read the update-notifier config file.