Update gitignore to ignore coverage directory
Update gitignore to ignore coverage directory

adriancole/zipkin,openzipkin/zipkin,adriancole/zipkin,openzipkin/zipkin,twitter/zipkin,adriancole/zipkin,openzipkin/zipkin,openzipkin/zipkin,openzipkin/zipkin,twitter/zipkin,twitter/zipkin,twitter/zipkin,adriancole/zipkin