DOC: to_datetime outdated example
With the new default of `errors='raise'`, the following section in the docs is not fully correctly phrased anymore: http://pandas-docs.github.io/pandas-docs-travis/timeseries.html#invalid-data. 

So I just removed that example of `to_datetime([1, '1'])` (as it now raises, which is less unexpected, and the new example already shows the three options).

@jreback BTW, as you can see in the docs, the example gives the following error message:

```
In [31]: to_datetime([1, '1'])
TypeError: invalid string coercion to datetime
```

That seems a bit a strange message?

E.g. if you only have strings, you get "Given date string not likely a datetime." (this sounds much clearer)
 yeh, that original example is an odd duck as you have an actual python object which is not convvertible by default (an integer). So the error message is 'correct', but prob misleading (as its bubbling up from somewhere)
