Rename mvm to flexible environment in SparkJava sample.

Managed VMs is now App Engine flexible environment.

We should at least rename the header to reduce confusion when people arrive here from https://cloud.google.com/java/.

managed_vms/sparkjava/README.md

@@ -1,7 +1,6 @@
-gcloud-java example using Managed VMs & SparkJava
-=================================================
+# SparkJava on App Engine Flexible Environment
 
-This app demonstrates how to use [`gcloud-java`'s Datastore client](https://github.com/GoogleCloudPlatform/gcloud-java/tree/master/gcloud-java-datastore#google-cloud-java-client-for-datastore) from within an [App Engine Managed VM](https://cloud.google.com/appengine/docs/java/managed-vms/) project using [SparkJava](http://sparkjava.com/). The app allows you to create and modify a database of "users", which contains their ID, name, and email information. 
+This app demonstrates how to use [`gcloud-java`'s Datastore client](https://github.com/GoogleCloudPlatform/gcloud-java/tree/master/gcloud-java-datastore#google-cloud-java-client-for-datastore) from within an [App Engine flexible environment](https://cloud.google.com/appengine/docs/flexible/java/hello-world) project using [SparkJava](http://sparkjava.com/). The app allows you to create and modify a database of "users", which contains their ID, name, and email information. 
 
 `gcloud-java` is an idiomatic Java client for [Google Cloud Platform](https://cloud.google.com/) services. Read more about the library [here](https://github.com/GoogleCloudPlatform/gcloud-java#google-cloud-java-client).