Fix error in Java MyPipelineStack (#354)

Overview
- For Java projects there is no `package.json` to install AWS-CDK. This
causes errors when attempting to deploy the pipeline as the `npm ci`
step depends on this file.
- Fixed the commands to `Arrays.asList("npm install -g aws-sdk", "cdk
  synth")` to correct this behavior.

Testing
- Created new pipeline following the updated steps and was successful in
  pipeline creation and deployment.

Relevant links
- https://docs.aws.amazon.com/cdk/api/latest/docs/pipelines-readme.html
- In the `Synth and sources` section this behavior is described.

Author: lpshanley