Update custom_easy_build_environment.md

doc.zih.tu-dresden.de/docs/software/custom_easy_build_environment.md

@@ -140,7 +140,7 @@ the latter will take precedence.
 The configuration used can be shown via:
 
 ```console
-marie@compute$ eb --showconfig
+marie@compute$ eb --show-config
 ```
 
 This shows all changed/non-default options while the parameter `--show-full-config` shows all options.