Rename doctest attribute standalone-crate into standalone_crate f…

…or coherency

core/src/panic/location.rs

@@ -44,7 +44,7 @@ impl<'a> Location<'a> {
     ///
     /// # Examples
     ///
-    /// ```standalone-crate
+    /// ```standalone_crate
     /// use std::panic::Location;
     ///
     /// /// Returns the [`Location`] at which it is called.