Change field name.

[yfhong]

Field name conflict with collectd json metric.

[elasticsearch-release]

Jenkins standing by to test this. If you aren't a maintainer, you can ignore this comment. Someone with commit access, please review this and clear it for Jenkins to run; then say 'jenkins, test it'.

[untergeek]

Changing a field name is a breaking change. This will need to be mentioned in the Changelog, the version number increased to the next major number, and thoroughly documented.

Can you please explain where the collision is? I understand that you have two field names colliding, but if they're both string values, why is that a conflict?

[jsvd]

this has been solved by #68