float parsing fix

```ruby
num = 30.0
("%0.#{13}g" % num).gsub(/0+$/, "")
#=> 3
num = 3 * 10**10
("%0.#{13}g" % num).gsub(/0+$/, "")
#=> 3
num = 3 * 10**12 + 0.1111111
("%0.#{13}g" % num).gsub(/0+$/, "")
#=> 3
num = 3 * 10**11 + 0.1111111
("%0.#{13}g" % num).gsub(/0+$/, "")
#=> 300000000000.1
```