preserve options.selector setting

This fixes a bug with the  $('input').validator({...}) usage suggested in the readme.

When the first input was validated on blur, options.selector was set to that input via `options.selector = options.selector || this;`. When a second input was validated, options.selector was still set to the first input, so the first input was re-validated instead of the second input.

My fix was to reset options.selector to the explicit setting after validations.validate(options) was done.