update rust toolchain

components/canvas/canvas_data.rs

@@ -455,7 +455,7 @@ impl<'a> CanvasData<'a> {
 
     pub fn restore_context_state(&mut self) {
         if let Some(state) = self.saved_states.pop() {
-            mem::replace(&mut self.state, state);
+            let _ = mem::replace(&mut self.state, state);
             self.drawtarget.set_transform(&self.state.transform);
             self.drawtarget.pop_clip();
         }

components/script/dom/response.rs

@@ -239,7 +239,7 @@ impl BodyOperations for Response {
         match body {
             NetTraitsResponseBody::Done(bytes) => Some(bytes),
             body => {
-                mem::replace(&mut *self.body.borrow_mut(), body);
+                let _ = mem::replace(&mut *self.body.borrow_mut(), body);
                 None
             },
         }

components/style/values/generics/calc.rs

@@ -337,7 +337,7 @@ impl<L: CalcNodeLeaf> CalcNode<L> {
             ($slot:expr) => {{
                 let dummy = Self::MinMax(Default::default(), MinMaxOp::Max);
                 let result = mem::replace($slot, dummy);
-                mem::replace(self, result);
+                let _ = mem::replace(self, result);
             }};
         }
         match *self {
@@ -464,7 +464,7 @@ impl<L: CalcNodeLeaf> CalcNode<L> {
                     replace_self_with!(&mut children[0]);
                 } else {
                     // Else put our simplified children back.
-                    mem::replace(children_slot, children.into_boxed_slice().into());
+                    let _ = mem::replace(children_slot, children.into_boxed_slice().into());
                 }
             },
             Self::Leaf(ref mut l) => {

rust-toolchain

@@ -1 +1 @@
-nightly-2020-04-08
+nightly-2020-05-15