fix spawn EINVAL error

fixes prebuild#68

bin.js

@@ -27,7 +27,7 @@ function build () {
     ]
   } catch (_) {}
 
-  proc.spawn(args[0], args.slice(1), { stdio: 'inherit' }).on('exit', function (code) {
+  proc.spawn(args[0], args.slice(1), { stdio: 'inherit', shell: true, windowsHide: true }).on('exit', function (code) {
     if (code || !process.argv[3]) process.exit(code)
     exec(process.argv[3]).on('exit', function (code) {
       process.exit(code)
@@ -45,15 +45,18 @@ function preinstall () {
 
 function exec (cmd) {
   if (process.platform !== 'win32') {
-    var shell = os.platform() === 'android' ? 'sh' : '/bin/sh'
-    return proc.spawn(shell, ['-c', '--', cmd], {
+    var shell = os.platform() === 'android' ? 'sh' : undefined
+    return proc.spawn(cmd, [], {
+      shell,
       stdio: 'inherit'
     })
   }
 
-  return proc.spawn(process.env.comspec || 'cmd.exe', ['/s', '/c', '"' + cmd + '"'], {
+  return proc.spawn(cmd, [], {
     windowsVerbatimArguments: true,
-    stdio: 'inherit'
+    stdio: 'inherit',
+    shell: true,
+    windowsHide: true
   })
 }