Limit ruby-kafka version because Producer API is changes. ref #210
Limit ruby-kafka version because Producer API is changes. ref #210

We will support ruby-kafka v0.7 in fluent-plugin-kafka v0.8.

Signed-off-by: Masahiro Nakagawa <0f51a8c574c157b13d3ee3d2579e24fcb2f5df0d@gmail.com>

htgc/fluent-plugin-kafka