undefined method force_encoding

error `v` not a String??? - Fixed

```
kladr.rb:59:in `block (3 levels) in convert': undefined method `force_encoding' for #<Date: 2011-01-21 ((2455583j,0s,0n),+0s,2299161j)> (NoMethodError)                                   | ETA:  --:--:--
	from kladr.rb:59:in `open'
	from kladr.rb:59:in `block (2 levels) in convert'
	from kladr.rb:54:in `each'
	from kladr.rb:54:in `block in convert'
	from /home/debadmin/.rvm/gems/ruby-2.1.0@rails403/gems/dbf-2.0.7/lib/dbf/table.rb:101:in `block in each'
	from /home/debadmin/.rvm/gems/ruby-2.1.0@rails403/gems/dbf-2.0.7/lib/dbf/table.rb:101:in `times'
	from /home/debadmin/.rvm/gems/ruby-2.1.0@rails403/gems/dbf-2.0.7/lib/dbf/table.rb:101:in `each'
	from kladr.rb:30:in `convert'
	from kladr.rb:75:in `block in <main>'
	from kladr.rb:75:in `glob'
	from kladr.rb:75:in `<main>'
```