Move .strip to after .pack in sanitize_value

Before:
````ruby
" whitespace and unicode #{128.chr('UTF-8')} ".strip.unpack('U*').select {|b| b < 127}.pack('U*')
#=> "whitespace and unicode "
````
After:
````ruby
" whitespace and unicode #{128.chr('UTF-8')} ".unpack('U*').select {|b| b < 127}.pack('U*').strip
#=> "whitespace and unicode"
````