update config.json

openlane/user_proj_example/config.json

diff --git a/openlane/user_proj_example/config.json b/openlane/user_proj_example/config.json
index 3f616d0..3c446f2 100644
--- a/openlane/user_proj_example/config.json
+++ b/openlane/user_proj_example/config.json
@@ -16,7 +16,7 @@
     "RUN_CVC": 1,
     "pdk::sky130*": {
         "FP_CORE_UTIL": 45,
-        "RT_MAX_LAYER": "{met4}",
+        "RT_MAX_LAYER": "met4",
         "scl::sky130_fd_sc_hd": {
             "CLOCK_PERIOD": 10
         },
@@ -38,7 +38,7 @@
         "STD_CELL_LIBRARY": "gf180mcu_fd_sc_mcu7t5v0",
         "CLOCK_PERIOD": 24.0,
         "FP_CORE_UTIL": 40,
-        "RT_MAX_LAYER": "{Metal4}",
+        "RT_MAX_LAYER": "Metal4",
         "SYNTH_MAX_FANOUT": 4,
         "PL_TARGET_DENSITY": 0.45
     }