Set webpack target property to "node" in case it is missing in the config

[HyperBrain]

This is a Feature Proposal

Description

It turned out in #274 , that, when the target: "node" property is missing in the webpack configuration, the compiles mostly work, but are missing the environment variables.
For the user this is not obvious, but can be checked by the plugin easily. It would be a great UX improvement, if the plugin could warn about the missing setting and set it to "node" automatically if absent.

Similar or dependent issue(s):

• All environment variables are missing  #274

Additional Data

• Serverless-Webpack Version you're using:
• Webpack version you're using:
• Serverless Framework Version you're using:
• Operating System:
• Stack Trace (if available):

[HyperBrain]

Released with 4.1.0