RubyKaigi 2018 LT の CFP 出した

次のような感じで RubyKaigi 2018 LT の CFP に出したよ。

## Improve JSON performance

I would like to talk my progress of daily contribution to Ruby world.
Last year, I talked about my performance improvement to Ruby core at RubyKaigi 2017.
I'm planing to talk the improvement to json gem as following with 5 minutes at RubyKaigi 2018 LT.


When my pull request will be merged, json gem performance will improve as 
JSON.parse()    -> 60.9 % faster
JSON.generate() -> 3.5 times faster

みんな大好きな JSON が速くなると、世界がよりよくなる・・・はず。


さっさと Pull Request がマージされたい( ˘ω˘)