Fix Dockerfile
Fix Dockerfile

* Change build artifact directory from build/maven to target/
  `docker builds` fail at 'mv
build/maven/aws-apigateway-*-jar-with-dependencies.jar
/aws-apigateway-importer.jar' because maven is
building into target/ instead.

* Do not attempt to remove /root/.m2
  The Maven Docker image exports /root/.m2 so `rm -rf ~/.m2` fails. See
https://github.com/carlossg/docker-maven/blob/8ab542b907e69c5269942bcc0915d8dffcc7e9fa/jdk-8/Dockerfile#L11
for reference.

awslabs/aws-apigateway-swagger-importer,awslabs/aws-apigateway-importer,awslabs/aws-apigateway-swagger-importer,ernesto9223/aws-apigateway-importer,ernesto9223/aws-apigateway-importer,awslabs/aws-apigateway-importer