Reword to avoid using either re-assignment or reassignment in errors

src/librustc_mir/borrow_check.rs

@@ -1161,7 +1161,7 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
         self.tcx.cannot_reassign_immutable(span,
                                            &self.describe_lvalue(lvalue),
                                            Origin::Mir)
-                .span_label(span, "re-assignment of immutable variable")
+                .span_label(span, "cannot assign twice to immutable variable")
                 .span_label(assigned_span, format!("first assignment to `{}`",
                                                    self.describe_lvalue(lvalue)))
                 .emit();

src/librustc_mir/util/borrowck_errors.rs

@@ -232,7 +232,7 @@ pub trait BorrowckErrors {
                                  -> DiagnosticBuilder
     {
         struct_span_err!(self, span, E0384,
-                         "re-assignment of immutable variable `{}`{OGN}",
+                         "cannot assign twice to immutable variable `{}`{OGN}",
                          desc, OGN=o)
     }