snakeyaml version in example conflicts with Cassandra

[will-sargent-eero]

When running the example from the docker image, the following exception prevents startup:

app-1         | 17:50:50.795 [main] INFO  o.a.c.config.YamlConfigurationLoader - Configuration location: file:/tmp/cassandra/cassandra-server.yaml
app-1         | Exception in thread "main" java.lang.NoSuchMethodError: org.yaml.snakeyaml.constructor.Constructor.<init>(Ljava/lang/Class;)V
app-1         | 	at org.apache.cassandra.config.YamlConfigurationLoader$CustomConstructor.<init>(YamlConfigurationLoader.java:139)
app-1         | 	at org.apache.cassandra.config.YamlConfigurationLoader.loadConfig(YamlConfigurationLoader.java:120)
app-1         | 	at org.apache.cassandra.config.YamlConfigurationLoader.loadConfig(YamlConfigurationLoader.java:101)
app-1         | 	at org.apache.cassandra.config.DatabaseDescriptor.loadConfig(DatabaseDescriptor.java:276)
app-1         | 	at org.apache.cassandra.config.DatabaseDescriptor.daemonInitialization(DatabaseDescriptor.java:152)
app-1         | 	at org.apache.cassandra.config.DatabaseDescriptor.daemonInitialization(DatabaseDescriptor.java:137)
app-1         | 	at org.cassandraunit.utils.EmbeddedCassandraServerHelper.startEmbeddedCassandra(EmbeddedCassandraServerHelper.java:145)
app-1         | 	at org.cassandraunit.utils.EmbeddedCassandraServerHelper.startEmbeddedCassandra(EmbeddedCassandraServerHelper.java:108)
app-1         | 	at org.cassandraunit.utils.EmbeddedCassandraServerHelper.startEmbeddedCassandra(EmbeddedCassandraServerHelper.java:92)
app-1         | 	at nl.pragmasoft.app.Main$.<clinit>(Main.scala:16)
app-1         | 	at nl.pragmasoft.app.Main.main(Main.scala)

I think this is because the hardcoded snakeyaml for prometheus at

https://github.com/jacum/akka-sensors/blob/master/project/Dependencies.scala#L44

conflicts with the snakeyaml 1.1 in Cassandra.