$ gem install leafy-metrics
Fetching: leafy-metrics-0.4.0-java.gem (100%)
  jar dependencies for leafy-metrics-0.4.0-java.gemspec . . .
      io.dropwizard.metrics:metrics-core:3.1.0
      io.dropwizard.metrics:metrics-graphite:3.1.0
      io.dropwizard.metrics:metrics-jvm:3.1.0
      org.slf4j:slf4j-simple:1.7.7
Successfully installed leafy-metrics-0.4.0-java
ERROR:  While executing gem ... (Psych::SyntaxError)
    (<unknown>): mapping values are not allowed here at line 13 column 151