Update failback.py

Example spell fix

Author: JayasilanJibm

SoftLayer/CLI/file/replication/failback.py

@@ -13,7 +13,7 @@
 def cli(env, volume_id):
     """Failback a file volume from the given replicant volume.
 
-    Exmaple::
+    Example::
         slcli file replica-failback 12345678
         This command performs failback operation for volume with ID 12345678.
 """