Update 03.modify_app.md

Replaced maverick to wrangler

Author: Jawon Song

docs/03.modify_app.md

@@ -20,7 +20,7 @@ This is an example Agave app `json` file from
   "name": "username-fastqc",
   "version": "0.11.7",
   "executionType": "HPC",
-  "executionSystem": "hpc-tacc-maverick-username",
+  "executionSystem": "hpc-tacc-wrangler-username",
   "parallelism": "SERIAL",
   "deploymentPath": "username/apps/fastqc-0.11.7",
   "deploymentSystem": "data-sd2e-projects-users",