refactor HTTParty::HashConversions.to_params

[rusikf]

1. I think using dangerous chop! is unnecessary , you can use this:

def self.to_params(hash)
 params = hash.to_hash.map { |k,v| normalize_param(k,v) }.join
 params.chop
end

2. Using params variable is not necessary, using chop in chain is more concise and used in the same way as map, join method
3. Tests are added in previous pr Create spec for HashConversion #367