"before all" hook: TypeError: callback is not a function

Hi!

Can't run abao simple test, I get the following errors (truncated):

```
1) "before all" hook
2) "after all" hook

0 passing (46ms)
2 failing

1) "before all" hook:
TypeError: callback is not a function
at /usr/local/lib/node_modules/abao/lib/hooks.coffee:76:16
at /usr/local/lib/node_modules/abao/node_modules/async/dist/async.js:3888:9
at /usr/local/lib/node_modules/abao/node_modules/async/dist/async.js:473:16
at replenish (/usr/local/lib/node_modules/abao/node_modules/async/dist/async.js:1006:25)
at /usr/local/lib/node_modules/abao/node_modules/async/dist/async.js:1016:9
at eachOfLimit (/usr/local/lib/node_modules/abao/node_modules/async/dist/async.js:1041:24)
...

2) "after all" hook:
TypeError: callback is not a function
at /usr/local/lib/node_modules/abao/lib/hooks.coffee:82:16
at /usr/local/lib/node_modules/abao/node_modules/async/dist/async.js:3888:9
...
```

Environment:

```
>$ node --version
v15.5.1
>$
>$ abao --version
0.5.0
```
RAML:

```
#%RAML 0.8
title: Fruits API
version: v1
baseUri: http://localhost:8080
/fruits:
get:
description: Get a list of fruits
responses:
200:
body:
application/json:
schema: |
[
description: 'string',
fruit: 'string'
]
example: |
{"description":"Winter fruit","name":"Apple"}
```
This is the output I get from the API to test:

```
>$ curl localhost:8080/fruits
[{"description":"Winter fruit","name":"Apple"},{"description":"Tropical fruit","name":"Pineapple"}]>
```

Please your help

Happy new year!