use `self.key_bindings` because it was mutably borrowed

While compiling ion:

   Compiling liner v0.4.4
warning[E0503]: cannot use `self.key_bindings` because it was mutably borrowed
  --> /home/xav/.cargo/registry/src/github.com-1ecc6299db9ec823/liner-0.4.4/src/context.rs:98:17
   |
96 |             let ed = try!(Editor::new_with_init_buffer(stdout, prompt, self, buffer));
   |                                                                        ---- borrow of `*self` occurs here
97 |             match self.key_bindings {
98 |                 KeyBindings::Emacs => Self::handle_keys(keymap::Emacs::new(ed), handler),
   |                 ^^^^^^^^^^^^^^^^^^ use of borrowed `*self`
99 |                 KeyBindings::Vi => Self::handle_keys(keymap::Vi::new(ed), handler),
   |                                                                      -- borrow later used here
   |
   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future