Update zone_delete.py

Example spell fix

Author: JayasilanJibm

SoftLayer/CLI/dns/zone_delete.py

@@ -16,7 +16,7 @@
 def cli(env, zone):
     """Delete zone.
 
-    Exmaple::
+    Example::
         slcli dns zone-delete ibm.com
         This command deletes a zone that is named ibm.com
 """