networks: css: Make button wider in network list

testing:
- Might this impact somewhere else (same form-button combination)?
- Yapf: not applicable.
- Flake8: without errors or warnings for changed files.
- (Unit) tests: run without errors.

Signed-off-by: Fioddor Superconcentrado <fioddor@gmail.com>
[sunil: Use min width instead of fixed width]
Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>

plinth/modules/networks/templates/networks_configuration.html

@@ -34,7 +34,7 @@
     }
 
     .form-action button {
-        width: 7em;
+        min-width: 7em;
     }
   </style>
 {% endblock %}