Fix parse mistake.

dmc-lib/src/parser.rs

@@ -397,7 +397,7 @@ impl<'a> Parser<'a> {
             match current.kind() {
                 TokenKind::Plus => {
                     self.advance(); // plus
-                    let rhs = self.expression()?;
+                    let rhs = self.suffix_expression()?;
                     let source_range =
                         SourceRange::new(result.source_range().start(), rhs.source_range().end());
                     result =