Substrate: build error: enum variants on type aliases are experimental

[xlc]

trying to build subkey

Compiling srml-grandpa v2.0.0 (/Users/bryan/Documents/projects/substrate/srml/grandpa)
   Compiling srml-babe v2.0.0 (/Users/bryan/Documents/projects/substrate/srml/babe)
error: enum variants on type aliases are experimental
   --> /Users/bryan/Documents/projects/srml/im-online/src/lib.rs:256:25
    |
256 |                 Self::deposit_event(Event::<T>::HeartbeatReceived(public.clone()));
    |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: add `#![feature(type_alias_enum_variants)]` to the crate attributes to enable

error: aborting due to previous error

error: Could not compile `srml-im-online`.
warning: build failed, waiting for other jobs to finish...
warning: struct is never constructed: `IndexedEvent`
   --> /Users/bryan/Documents/projects/substrate/srml/contracts/src/exec.rs:193:1
    |
193 | pub struct IndexedEvent<T: Trait> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: #[warn(dead_code)] on by default

error: build failed

warning: build failed, waiting for other jobs to finish...
error: build failed
bryan@bryan-mbp:subkey ((409f5aa10...)) $ cargo -V
cargo 1.37.0 (9edd08916 2019-08-02)
bryan@bryan-mbp:subkey ((409f5aa10...)) $ rustc -V
rustc 1.37.0 (eae3437df 2019-08-13)

[xlc]

need rustup update nightly