Logspout generating invalid GELF headers

[averri]

Steps to reproduce

Start Logstash using Gelf input and print logs to Stdout:

docker run -p 12201:12201/udp logstash -e 'input{ gelf{ } } output{ stdout { codec => rubydebug } }'

On another terminal, start the Logspout application:

docker run  -v /var/run/docker.sock:/var/run/docker.sock -d micahhausler/logspout:gelf  gelf://192.168.99.100:12201

Log a message from any container:

docker run --rm busybox echo Hello

Logstash will not recognize the GELF header:

{:timestamp=>"2016-08-09T10:02:00.844000+0000", :message=>"Gelfd failed to parse a message skipping", :exception=>#<Gelfd::UnknownHeaderError: Could not find pa
rser for header: [123, 34]>, :backtrace=>["/opt/logstash/vendor/bundle/jruby/1.9/gems/gelfd-0.2.0/lib/gelfd/parser.rb:14:in `parse'", "/opt/logstash/vendor/bund
le/jruby/1.9/gems/logstash-input-gelf-2.0.7/lib/logstash/inputs/gelf.rb:104:in `udp_listener'", "/opt/logstash/vendor/bundle/jruby/1.9/gems/logstash-input-gelf-
2.0.7/lib/logstash/inputs/gelf.rb:77:in `run'", "/opt/logstash/vendor/bundle/jruby/1.9/gems/logstash-core-2.3.4-java/lib/logstash/pipeline.rb:342:in `inputworke
r'", "/opt/logstash/vendor/bundle/jruby/1.9/gems/logstash-core-2.3.4-java/lib/logstash/pipeline.rb:336:in `start_input'"], :level=>:warn}