Pass PATH environment in the child_process.fork spec.

The uv_spawn under Windows requires the PATH environment variable to be
there, otherwise it would throw a 203 system error, it should be a bug
of node.

spec/node/child_process.coffee

@@ -23,7 +23,7 @@ describe 'child_process', ->
     it 'should work in forked process when options.env is specifed', (done) ->
       child = child_process.fork path.join(fixtures, 'module', 'fork_ping.js'),
                                  [],
-                                 env: {test: 'somevar'}
+                                 path: process.env['PATH']
       child.on 'message', (msg) ->
         assert.equal msg, 'message'
         done()