preserve "use strict" directive when wrapping CommonJS module

Fixes #39

Please review these changes, @eush77. :)

@buzzdecafe, @CrossEye: I'm converging via `R.apply` here, which suggests that `R.call` would be a useful addition to Ramda. In this example it'd obviate the need for `R.of`—and thus `R.pipe`—in the second branch:

```coffeescript
R.converge(
  R.call
  R.pipe R.prop('indent'), R.length, indentN
  wrap.coffee
)
```