fixes bug when using new ..()

Thank you for implementing a grunt-agnostic version of neuter. I was having some trouble if the "neutered" files contain a new statement.

For example:

    var test = new String('test');

The error message:

    PATH_DELETED\node_modules\gulp-neuter\node_modules\neuter\lib\scanner.js:220
                                    if (childNode.type === 'FunctionDeclaration' ||
                                                 ^
    TypeError: Cannot read property 'type' of undefined
        at Immediate._onImmediate (PATH_DELETED\node_modules\gulp-neuter\node_modules\neuter\lib\scanner.js:220:18)
        at processImmediate [as _immediateCallback] (timers.js:374:17)

I'm using node v0.11.12.