doc example doesn't work

[tisdall]

Trying out an example in the docs I get the following:

>>> ranged_int = colander.SchemaNode(
...     schema_type=colander.Int,
...     validator=colander.Range(0, 10),
...     default=10,
...     title='Ranged Int'
...     )
Traceback (most recent call last):
  File "<stdin>", line 5, in <module>
  File "/sites/metrics_dev/env/lib/python3.4/site-packages/colander/__init__.py", line 1817, in __init__
    self.typ = self.schema_type()
  File "/sites/metrics_dev/env/lib/python3.4/site-packages/colander/__init__.py", line 1833, in schema_type
    'Schema node construction without a typ argument or '
NotImplementedError: Schema node construction without a typ argument or a schema_type() callable present on the node class 

related to #229

[mmerickel]

The doc example is fixed. Sorry but I don't want to add doctests, they're not a pattern I'm comfortable with especially if they don't work with the existing code-block directive.