Use taskkill instead of .kill() on Windows

Solution to arjunmehta#10
Inspired by nodejs/node#3675

lib/Spawn.js

@@ -1,4 +1,4 @@
-var spawn = require('child_process').spawn;
+var child_process = require('child_process');
 
 function Spawn(stream, command, args, name, output) {
   var exited = false;
@@ -13,7 +13,7 @@ function Spawn(stream, command, args, name, output) {
     };
   }
 
-  spawnedProcess = spawn(command, args, options);
+  spawnedProcess = child_process.spawn(command, args, options);
 
   this.id = name;
 
@@ -52,7 +52,13 @@ function Spawn(stream, command, args, name, output) {
 
   process.on('exit', function(code) {
     if (exited === false) {
-      spawnedProcess.kill();
+      if (process.platform === 'win32') {
+        // Workaround for kill() not propagating to children of the cmd.exe we launched
+        // see https://github.com/nodejs/node/issues/3675#issuecomment-288578092
+        child_process.exec('taskkill /F /T /PID ' + spawnedProcess.pid);
+      } else {
+        spawnedProcess.kill();
+      }
     }
   });