www/firefox-esr: unbreak with rust 1.37

error: trait objects without an explicit dyn are deprecated

--> gfx/webrender_bindings/src/bindings.rs:471:28
 |

471 | fn clone(&self) -> Box<RenderNotifier> {

|                            ^^^^^^^^^^^^^^ help: use `dyn`: `dyn RenderNotifier`
|

note: lint level defined here

--> gfx/webrender_bindings/src/lib.rs:5:9
 |

5 | #![deny(warnings)]

|         ^^^^^^^^
= note: #[deny(bare_trait_objects)] implied by #[deny(warnings)]

error: trait objects without an explicit dyn are deprecated

--> gfx/webrender_bindings/src/bindings.rs:736:30
 |

736 | let recorder: Option<Box<ApiRecordingReceiver>> = if unsafe { gfx_use_wrench() } {

|                              ^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn ApiRecordingReceiver`

error: trait objects without an explicit dyn are deprecated

--> gfx/webrender_bindings/src/moz2d_renderer.rs:98:28
 |

98 | resources: &BlobImageResources,

|                            ^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn BlobImageResources`

error: trait objects without an explicit dyn are deprecated

--> gfx/webrender_bindings/src/moz2d_renderer.rs:136:65
 |

136 | fn process_fonts(mut extra_data: BufReader, resources: &BlobImageResources) {

|                                                                 ^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn BlobImageResources`

error: aborting due to 4 previous errors
error: Could not compile webrender_bindings.

Reported by: tobik
Obtained from: upstream (Firefox 68)