Update njs module from 0.3.9 to 0.4.0.

<ChangeLog>

*) Feature: added js_import directive.

*) Feature: added support for multi-value headers in r.headersOut.

*) Improvement: iteration over r.headersOut with special headers.

*) Improvement: iteration over r.headersOut with duplicates.

*) Change: r.responseBody property handler now returns "undefined"

instead of throwing an exception if response body is not available.

Core:

*) Feature: added script arguments support in CLI.

*) Feature: converting externals values to native js objects.

*) Bugfix: fixed NULL-pointer dereference in "proto" property

handler.

*) Bugfix: fixed handling of no-newline at the end of the script.

*) Bugfix: fixed RegExp() constructor with empty pattern and

non-empty flags.

*) Bugfix: fixed String.prototype.replace() when function

returns non-string.

*) Bugfix: fixed reading of pseudofiles in "fs".

</ChangeLog>