Lib doesn't build due to a change in serde

[fafk]

Serde changed the visibility of mod export from public to private and it breaks refinery.

serde-rs/serde@dd1f4b4 line 275

error[E0603]: module `export` is private
   --> /Users/fafk/.cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/refinery-core-0.3.2/src/runner.rs:11:12
    |
11  | use serde::export::Formatter;
    |            ^^^^^^ private module
    |
note: the module `export` is defined here
   --> /Users/fafk/.cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/serde-1.0.119/src/lib.rs:275:5
    |
275 | use self::__private as export;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0603`.
error: could not compile `refinery-core`

[jxs]

Hi, this has been addressed in master: #149, but i will release a fix ASAP.
thanks

[jxs]

released refinery_core:0.5.1
do cargo update to update Cargo.lock to use it