add Node.js 8 to Travis CI (#2086)

- explicitly terminate `test/jetstream.js` upon completion
- log verbose output from `test/benchmark.js` & `test/jetstream.js`
- remove obsolete workaround for Travis CI

.travis.yml

@@ -4,6 +4,7 @@ node_js:
     - "0.12"
     - "4"
     - "6"
+    - "8"
 env:
     - UGLIFYJS_TEST_ALL=1
 matrix:

test/jetstream.js

@@ -64,6 +64,7 @@ if (typeof phantom == "undefined") {
                     server.close();
                     if (code) throw new Error("JetStream failed!");
                     console.log("JetStream completed successfully.");
+                    process.exit(0);
                 });
             });
         }

test/mocha/release.js

@@ -4,13 +4,9 @@ var spawn = require("child_process").spawn;
 if (!process.env.UGLIFYJS_TEST_ALL) return;
 
 function run(command, args, done) {
-    var id = setInterval(function() {
-        process.stdout.write("\0");
-    }, 5 * 60 * 1000);
     spawn(command, args, {
-        stdio: "ignore"
+        stdio: [ "ignore", 1, 2 ]
     }).on("exit", function(code) {
-        clearInterval(id);
         assert.strictEqual(code, 0);
         done();
     });