Update dependencies
Update dependencies

Ran `cargo update`. This gets us clang-sys version 0.15.2, which contains some
fixes for finding the appropriate libclang.so.

Fixes #671

rust-lang/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen