can't omit precision for a Float about dentaku

[rubysolo]

This is fixed on master, but I haven't cut a new gem version yet -- sorry about that!

[1] pry(main)> c = Dentaku::Calculator.new
=> #<Dentaku::Calculator:0x007fcbb91b9270 @ast_cache={}, @memory={}, @tokenizer=#<Dentaku::Tokenizer:0x007fcbb91b9860>>
[2] pry(main)> c.store({"cost_of_eletricity"=>0.253, "scrn_native_vert"=>10.0, "connectstodlnaserver"=>100.0})
=> #<Dentaku::Calculator:0x007fcbb91b9270 @ast_cache={}, @memory={"cost_of_eletricity"=>0.253, "scrn_native_vert"=>10.0, "connectstodlnaserver"=>100.0}, @tokenizer=#<Dentaku::Tokenizer:0x007fcbb91b9860>>
[3] pry(main)> c.evaluate("( ( 1 + scrn_native_vert ) * connectstodlnaserver ) / cost_of_eletricity")
=> #<BigDecimal:7fcbb886e738,'0.4347826086 957E4',18(36)>