WARNING messages during mvn package

[arun-gupta]

Packaging the deployment gives the following warning message:

ubuntu@ip-172-31-47-216:~/realworld-serverless-application$ mvn clean package -DpackageBucket=arun-sam-deployments
[INFO] Scanning for projects...
[WARNING] 
[WARNING] Some problems were encountered while building the effective model for software.amazon.serverless:aws-ssm-caching-client:jar:1.0.0
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 20, column 21
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-deploy-plugin is missing. @ line 46, column 21
[WARNING] 
[WARNING] Some problems were encountered while building the effective model for com.amazonaws.serverless:realworld-serverless-application-backend:jar:0.1.5
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-deploy-plugin is missing. @ line 311, column 15
[WARNING] 
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING] 
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING] 

We should clean this up.

[jlhood]

Can be fixed by adding an explicit version here: https://github.com/awslabs/realworld-serverless-application/blob/850ddf56764e59e1dd4ca2c40fd5bc8130061313/backend/pom.xml#L312