Update Crowd.php

update for new api . the parameter `encryptedCredential` can not be null.

```
<xsd:complexType name="PasswordCredential">
<xsd:sequence>
<xsd:element minOccurs="0" name="credential" nillable="true" type="xsd:string"/>
<xsd:element minOccurs="0" name="encryptedCredential" type="xsd:boolean"/>
</xsd:sequence>
</xsd:complexType>
```