address code review comments

Author: gaurikholkar

src/librustc_mir/borrow_check/mod.rs

@@ -1566,7 +1566,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
 
                 if place != place_err {
                     if let Some(name) = self.describe_place(place_err) {
-                        err.note(&format!("Value not mutable causing this error: `{}`", name));
+                        err.note(&format!("value not mutable causing this error: `{}`", name));
                     }
                 }
 
@@ -1619,13 +1619,13 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                             err.span_label(span, sec_span);
                         }
                         err.emit()
-                    }else{
+                    } else {
                         let item_msg_ = self.get_main_error_message(place);
                         let mut err = self.tcx.cannot_assign(span, &item_msg_, Origin::Mir, false);
                         err.span_label(span, "cannot mutate");
                         if place != place_err {
                             if let Some(name) = self.describe_place(place_err) {
-                                err.note(&format!("Value not mutable causing this error: `{}`",
+                                err.note(&format!("value not mutable causing this error: `{}`",
                                                   name));
                             }
                         }

src/test/ui/nll/issue-47388.rs

@@ -15,6 +15,6 @@ struct FancyNum {
 fn main() {
     let mut fancy = FancyNum{ num: 5 };
     let fancy_ref = &(&mut fancy);
-    fancy_ref.num = 6;
+    fancy_ref.num = 6; //~^ ERROR E0594
     println!("{}", fancy_ref.num);
 }

src/test/ui/nll/issue-47388.stderr

@@ -3,7 +3,7 @@ error[E0594]: cannot assign through `&`-reference `fancy_ref`
    |
 LL |     let fancy_ref = &(&mut fancy);
    |                     ------------- help: consider changing this to be a mutable reference: `&mut`
-LL |     fancy_ref.num = 6;
+LL |     fancy_ref.num = 6; //~^ ERROR E0594
    |     ^^^^^^^^^^^^^^^^^ cannot assign through `&`-reference
 
 error: aborting due to previous error