#14 Implemented option to preinstall yums before bundling gem

Author: navarasu

lib/bundle.js

@@ -44,9 +44,22 @@ function bundleInstall(){
     if (ps.error && ps.error.code === 'ENOENT') {
       throw new Error('docker command not found');
     }
+    let buildDocker = false;
     if (this.options.docker_file) {
       fs.copySync(path.join(this.servicePath, this.options.docker_file),
                   path.join(this.ruby_layer,'Dockerfile'))
+      buildDocker = true
+    }else if (this.options.docker_yums) {
+      docker_steps =['FROM lambci/lambda:build-'+this.serverless.service.provider.runtime]
+      this.options.docker_yums.forEach(function(package_name) {
+        docker_steps.push('RUN yum install -y '+package_name)
+      })
+      docker_steps.push('RUN gem update bundler')
+      docker_steps.push('CMD "/bin/bash"')
+      fs.writeFileSync(path.join(this.ruby_layer,'Dockerfile'),docker_steps.join('\n'))
+      buildDocker = true
+    }
+    if (buildDocker) {
       docker_name ='ruby-layer:docker'
       docker(['build', '-t', docker_name, '-f', 'Dockerfile', '.'], options,this.cli)
     }