Add lambda to clean.R

The output:

```s
library(fpp)
lambda <- BoxCox.lambda(a10)
a10[120]
```

```
## [1] 9.962
```

```s
a10[120] <- NA
na.interp(a10)[120]
```

```
## [1] 10.44
```

```s
na.interp(a10, lambda = lambda)[120]
```

```
## [1] 10.5
```

```s
a10[120] <- 100
tsoutliers(a10)
```

```
## $index
## [1] 120 187 199 201 204
## 
## $replacements
## [1] 10.46 24.11 27.80 22.98 22.52
```

```s
tsoutliers(a10, lambda = lambda)
```

```
## $index
## [1] 120
## 
## $replacements
## [1] 10.5
```