Properly worded diagnostic message

Author: oli-obk

src/librustc_mir/transform/qualify_consts.rs

@@ -1340,7 +1340,7 @@ impl MirPass for QualifyAndPromoteConstants {
                     let mut error = tcx.sess.struct_span_err(
                         span,
                         &format!(
-                            "new features like let bindings are not permitted in {} \
+                            "new features like let bindings are not permitted in {}s \
                             which also use short circuiting operators",
                             mode,
                         ),

src/test/ui/consts/const_short_circuit.stderr

@@ -1,4 +1,4 @@
-error: new features like let bindings are not permitted in constant which also use short circuiting operators
+error: new features like let bindings are not permitted in constants which also use short circuiting operators
   --> $DIR/const_short_circuit.rs:6:9
    |
 LL |     let mut x = true && false;
@@ -10,7 +10,7 @@ note: use of `&&` operator here
 LL |     let mut x = true && false;
    |                      ^^
 
-error: new features like let bindings are not permitted in constant which also use short circuiting operators
+error: new features like let bindings are not permitted in constants which also use short circuiting operators
   --> $DIR/const_short_circuit.rs:11:9
    |
 LL |     let x = true && false;