When using SLS_DEBUG environment variable output pip requirements command (#222)

closes #169

Author: twonds

lib/pip.js

@@ -129,8 +129,11 @@ function installRequirements(
     const slimCmd = getSlimPackageCommands(options, preparedPath);
     cmdOptions.push(...slimCmd);
   }
-
-  const res = spawnSync(cmd, cmdOptions, { cwd: servicePath, shell: true });
+  let spawnArgs = { cwd: servicePath, shell: true };
+  if (process.env.SLS_DEBUG) {
+    spawnArgs.stdio = 'inherit';
+  }
+  const res = spawnSync(cmd, cmdOptions, spawnArgs);
   if (res.error) {
     if (res.error.code === 'ENOENT') {
       if (options.dockerizePip) {