Fix pattern for classes extending SoapClient.

As I see it the current pattern has two problems:

- It does not match \SoapClient
- It matches any non-word characters after SoapClient. Thus line breaks and the beginning of docblocks are included and replaced.

One problem I have seen after this change is that `VCR\Util\Soap\SoapClient` is updated as well. I have fixed this locally by adding the path to the blacklist, but I am not sure whether this is the right way to go about this.