Corrected the Pattern Matching on class members example in basics2.textile

The existing code:

```scala
def calcType(calc: Calculator) = calc match {
  case calc.brand == "hp" && calc.model == "20B" => "financial"
  case calc.brand == "hp" && calc.model == "48G" => "scientific"
  case calc.brand == "hp" && calc.model == "30B" => "business"
  case _ => "unknown"
}
```
Will produce the following errors.
```
<console>:13: error: not found: value &&
         case calc.brand == "hp" && calc.model == "20B" => "financial"
                                 ^
<console>:14: error: not found: value &&
         case calc.brand == "hp" && calc.model == "48G" => "scientific"
                                 ^
<console>:15: error: not found: value &&
         case calc.brand == "hp" && calc.model == "30B" => "business"
                                 ^
```

The cases should be converted to use guards.