feat: setting runConcurrently to true enables concurrency

ref pnpm/pnpm#1578

Author: zkochan

README.md

@@ -42,6 +42,7 @@ jump in if you'd like to, or even ask us questions if something isn't clear.
 
 * `opts.stdio` - the [stdio](https://nodejs.org/api/child_process.html#child_process_options_stdio)
 passed to the child process. `[0, 1, 2]` by default.
+* `opts.runConcurrently` - *Boolean* - `false` by default. If `true`, lifecycle scripts may run concurrently.
 
 ##### Example
 

index.js

@@ -224,12 +224,14 @@ function dequeue () {
 }
 
 function runCmd (note, cmd, pkg, env, stage, wd, opts, cb) {
-  if (running) {
-    queue.push([note, cmd, pkg, env, stage, wd, opts, cb])
-    return
-  }
+  if (opts.runConcurrently !== true) {
+    if (running) {
+      queue.push([note, cmd, pkg, env, stage, wd, opts, cb])
+      return
+    }
 
-  running = true
+    running = true
+  }
   opts.log.pause()
   var unsafe = opts.unsafePerm
   var user = unsafe ? null : opts.user