Update error message to be clearer

Author: GuillaumeGomez

clippy_lints/src/incompatible_msrv.rs

@@ -99,7 +99,7 @@ impl IncompatibleMsrv {
             INCOMPATIBLE_MSRV,
             span,
             &format!(
-                "current MSRV is `{}` but this item is stable since `{version}`",
+                "current MSRV (Minimum Supported Rust Version) is `{}` but this item is stable since `{version}`",
                 self.msrv
             ),
         );

tests/ui/incompatible_msrv.rs

@@ -13,11 +13,11 @@ fn foo() {
     assert_eq!(map.entry("poneyland").key(), &"poneyland");
     if let Entry::Vacant(v) = map.entry("poneyland") {
         v.into_key();
-        //~^ ERROR:  MSRV is `1.3.0` but this item is stable since `1.12.0`
+        //~^ ERROR: is `1.3.0` but this item is stable since `1.12.0`
     }
     // Should warn for `sleep` but not for `Duration` (which was added in `1.3.0`).
     sleep(Duration::new(1, 0));
-    //~^ ERROR:  MSRV is `1.3.0` but this item is stable since `1.4.0`
+    //~^ ERROR: is `1.3.0` but this item is stable since `1.4.0`
 }
 
 fn main() {}

tests/ui/incompatible_msrv.stderr

@@ -1,4 +1,4 @@
-error: current MSRV is `1.3.0` but this item is stable since `1.10.0`
+error: current MSRV (Minimum Supported Rust Version) is `1.3.0` but this item is stable since `1.10.0`
   --> $DIR/incompatible_msrv.rs:13:39
    |
 LL |     assert_eq!(map.entry("poneyland").key(), &"poneyland");
@@ -7,13 +7,13 @@ LL |     assert_eq!(map.entry("poneyland").key(), &"poneyland");
    = note: `-D clippy::incompatible-msrv` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::incompatible_msrv)]`
 
-error: current MSRV is `1.3.0` but this item is stable since `1.12.0`
+error: current MSRV (Minimum Supported Rust Version) is `1.3.0` but this item is stable since `1.12.0`
   --> $DIR/incompatible_msrv.rs:15:11
    |
 LL |         v.into_key();
    |           ^^^^^^^^^^
 
-error: current MSRV is `1.3.0` but this item is stable since `1.4.0`
+error: current MSRV (Minimum Supported Rust Version) is `1.3.0` but this item is stable since `1.4.0`
   --> $DIR/incompatible_msrv.rs:19:5
    |
 LL |     sleep(Duration::new(1, 0));