Fix RuntimeError: can't modify frozen Addressable::URI

```ruby
irb(main):011:0> user.website
RuntimeError: can't modify frozen Addressable::URI
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/addressable-2.3.6/lib/addressable/uri.rb:1658:in `normalized_fragment'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/addressable-2.3.6/lib/addressable/uri.rb:823:in `freeze'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/memoizable-0.4.2/lib/memoizable.rb:17:in `block in <module:Memoizable>'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/memoizable-0.4.2/lib/memoizable/method_builder.rb:117:in `call'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/memoizable-0.4.2/lib/memoizable/method_builder.rb:117:in `block (3 levels) in create_memoized_method'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/memoizable-0.4.2/lib/memoizable/memory.rb:63:in `block (3 levels) in fetch'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/thread_safe-0.3.4/lib/thread_safe/cache.rb:58:in `fetch'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/memoizable-0.4.2/lib/memoizable/memory.rb:62:in `block (2 levels) in fetch'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/memoizable-0.4.2/lib/memoizable/memory.rb:61:in `block in fetch'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/thread_safe-0.3.4/lib/thread_safe/cache.rb:58:in `fetch'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/memoizable-0.4.2/lib/memoizable/memory.rb:60:in `fetch'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/memoizable-0.4.2/lib/memoizable/method_builder.rb:116:in `block (2 levels) in create_memoized_method'
	from (irb):11
	from /usr/local/var/rbenv/versions/2.1.2/bin/irb:11:in `<main>'
```