fix typo

src/frontend/src/optimizer/plan_expr_rewriter/cse_rewriter.rs

@@ -10,7 +10,7 @@
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
-// limitations under the License.use std::collections::HashMap;
+// limitations under the License.
 
 use std::collections::HashMap;