Add dyn to areas of core.

[kitsonk]

Nightly Rust complains with the following:

error: trait objects without an explicit `dyn` are deprecated
  --> ../../core/isolate.rs:71:19
   |
71 | type DispatchFn = Fn(&[u8], Option<PinnedBuf>) -> Op;
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(&[u8], Option<PinnedBuf>) -> Op`
   |
   = note: `-D bare-trait-objects` implied by `-D warnings`

error: trait objects without an explicit `dyn` are deprecated
  --> ../../core/isolate.rs:74:20
   |
74 | type DynImportFn = Fn(&str, &str) -> DynImportFuture;
   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(&str, &str) -> DynImportFuture`

error: trait objects without an explicit `dyn` are deprecated
   --> ../../core/modules.rs:598:32
    |
598 |     fn cause(&self) -> Option<&Error> {
    |                                ^^^^^ help: use `dyn`: `dyn Error`

error: aborting due to 3 previous errors

This patch fixes it and should be supported by earlier versions of Rust. (I had to update to a recent version of nightly because master has something that is triggering a bug in RLS, updating to a more recent version of nightly fixed that).

[95th]

One more error on Nightly (2019-06-17):

error[E0283]: type annotations required: cannot resolve `std::string::String: std::convert::AsRef<_>`
  --> ../../cli\repl.rs:97:44
   |
97 |         self.editor.add_history_entry(line.as_ref());
   |                                            ^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0283`.
ninja: build stopped: subcommand failed.

Fix:

self.editor.add_history_entry(&line);

[kitsonk]

In my other branch @ry suggested:

self.editor.add_history_entry(line.clone());

which is now reflected in this PR and rebased on master.

[95th]

I think cloning is not required because if you look at the rustyline's History implementation, it calls line.into which creates a new instance from the passed reference anyways.

[ry]

Hm I'm not sure what was happening on the other branch - I had to make that change to get it to compile locally... but if this is passing CI, I think it would be better left as is.

[ry]

Otherwise LGTM.

[kitsonk]

I changed it to &line in the other branch and you pushed a commit to line.clone().

[95th]

@kitsonk &line doesn't work in current stable and as_ref doesn't in nightly. Looks like a bug in Rust.

EDIT:
(Apparantly this is expected behavior as per rust-lang/rust#59825)

[95th]

For now, we can use verbose turbofish, which works on both:

self.editor.add_history_entry(AsRef::<str>::as_ref(&line))

[kitsonk]

@95th What is wrong with clone? It works in both. Probably best not to leak the reference anyways. The lifetime of line is suspect IMO.

[95th]

@kitsonk Nothing wrong. Just that the cloned instance is discarded in the method. I guess clone is fine here because it works without much noise.

[ry]

LGTM - not sure what the deal with the as_ref is but the clone works and is very far from a hot path.