Fix too many underscore for __custom_func (#794)

* Fix too many underscore for __custom_func

* Fix typo of too many leading underscores in docs

bash_completions.go

@@ -134,7 +134,7 @@ __%[1]s_handle_reply()
 			__%[1]s_custom_func
 		else
 			# otherwise fall back to unqualified for compatibility
-			declare -F ___custom_func >/dev/null && __custom_func
+			declare -F __custom_func >/dev/null && __custom_func
 		fi
     fi
 

bash_completions.md

@@ -109,7 +109,7 @@ Find more information at https://github.com/GoogleCloudPlatform/kubernetes.`,
 }
 ```
 
-The `BashCompletionFunction` option is really only valid/useful on the root command. Doing the above will cause `___kubectl_custom_func()` (`__<command-use>_custom_func()`) to be called when the built in processor was unable to find a solution. In the case of kubernetes a valid command might look something like `kubectl get pod [mypod]`. If you type `kubectl get pod [tab][tab]` the `__kubectl_customc_func()` will run because the cobra.Command only understood "kubectl" and "get." `__kubectl_custom_func()` will see that the cobra.Command is "kubectl_get" and will thus call another helper `__kubectl_get_resource()`.  `__kubectl_get_resource` will look at the 'nouns' collected. In our example the only noun will be `pod`.  So it will call `__kubectl_parse_get pod`.  `__kubectl_parse_get` will actually call out to kubernetes and get any pods.  It will then set `COMPREPLY` to valid pods!
+The `BashCompletionFunction` option is really only valid/useful on the root command. Doing the above will cause `__kubectl_custom_func()` (`__<command-use>_custom_func()`) to be called when the built in processor was unable to find a solution. In the case of kubernetes a valid command might look something like `kubectl get pod [mypod]`. If you type `kubectl get pod [tab][tab]` the `__kubectl_customc_func()` will run because the cobra.Command only understood "kubectl" and "get." `__kubectl_custom_func()` will see that the cobra.Command is "kubectl_get" and will thus call another helper `__kubectl_get_resource()`.  `__kubectl_get_resource` will look at the 'nouns' collected. In our example the only noun will be `pod`.  So it will call `__kubectl_parse_get pod`.  `__kubectl_parse_get` will actually call out to kubernetes and get any pods.  It will then set `COMPREPLY` to valid pods!
 
 ## Have the completions code complete your 'nouns'