Update crowdsales.adoc fix invalid conversion (#2026)

Code sample for MyCrowdsaleDeployer causes TypeError:
```
browser/MyCrowdsaleDeployer.sol:21:13: TypeError: Invalid type for argument in function call. 
Invalid implicit conversion from address to contract IERC20 requested.
            address(token)            // the token
            ^------------^
```
Change: 
```solidity
address(token)   // the token
```
To:
```solidity
token   // the token
```

Reported by community member in the forum: https://forum.openzeppelin.com/t/invalid-implicit-conversion-from-address-to-contract-ierc20-requested/1937

docs/modules/ROOT/pages/crowdsales.adoc

@@ -120,7 +120,7 @@ contract MyCrowdsaleDeployer {
         Crowdsale crowdsale = new MyCrowdsale(
             1,               // rate, still in TKNbits
             msg.sender,      // send Ether to the deployer
-            address(token)   // the token
+            token            // the token
         );
         // transfer the minter role from this contract (the default)
         // to the crowdsale, so it can mint tokens