Elasticsearch char_filter replace any character with whitespace?

I'm using elasticsearch for my Ruby on Rails application. I want to use char_filter to replace some characters with whitepace. In tutorial of elasticsearch it says something like: ``` "mappings" : ["ph=>f", "qu=>q"] ``` I've tried the following: ``` "mappings" : ["ph=>\s", "qu=>\s"] ``` However it does not seem to work. Any ideas guys?