[Bug] Fix nodejs npm build step (#112)

## Summary
Quick fix nodejs npm build step, as the command is different between npm
and yarn. This needs to go in before the next release.

## How was it tested?
go test ./...

Author: LucilleH

planner/languages/javascript/nodejs_planner.go

@@ -131,16 +131,18 @@ func (p *Planner) inputFiles(srcDir string) []string {
 
 func (p *Planner) buildCommand(pkgManager string, project *nodeProject) string {
 	buildScript := project.Scripts.Build
+	defaultBuildCmd := "npm run build"
 	postBuildCmdHook := "npm prune --production"
 
 	if pkgManager == "yarn" {
+		defaultBuildCmd = "yarn build"
 		postBuildCmdHook = "yarn install --production --ignore-scripts --prefer-offline"
 	}
 	if buildScript == "" {
 		return postBuildCmdHook
 	}
 
-	return fmt.Sprintf("%s build && %s", pkgManager, postBuildCmdHook)
+	return fmt.Sprintf("%s && %s", defaultBuildCmd, postBuildCmdHook)
 }
 
 func (p *Planner) startCommand(pkgManager string, project *nodeProject) string {

testdata/nodejs/nodejs-npm/package.json

@@ -1,5 +1,9 @@
 {
   "name": "nodejs-npm",
   "main": "index.js",
+  "scripts": {
+    "build": "echo building...",
+    "start": "node index.js"
+  },
   "dependencies": {}
 }

testdata/nodejs/nodejs-npm/plan.json

@@ -7,13 +7,13 @@
     ]
   },
   "build_stage": {
-    "command": "npm prune --production",
+    "command": "npm run build && npm prune --production",
     "input_files": [
       "."
     ]
   },
   "start_stage": {
-    "command": "node index.js",
+    "command": "npm start",
     "input_files": [
       "."
     ]