[stage/update] Handle putting/deleting files in series

Bug:

    Handling the two tasks of deleting and putting files
    in parallel, on the same connection, causes issue
    as commands to handle each scenario are passed over
    and are persisted to the following actions.

    Since the same connection is used, we need some order
    in handling the files

Fix:

    The actions are handled in series. First, put then delete.
    Not parallel.

    Each of the files, in the actions, are handled in series.
    One file after the other. Not all at the same time.

References:

    * Sending multiple files: sergi/jsftp#66

lib/stages/update.js

@@ -27,7 +27,7 @@ const filelist = require('../filelist');
 exports = module.exports = function update(globals, state, next) {
     // push the changed files
     function push(actionDone) {
-        async.each(state.diffs.changed, function(filename, done) {
+        async.eachSeries(state.diffs.changed, function(filename, done) {
             var filepath = path.join(state.remotedir.path, filename);
             globals.ftp.put(state.localdir.buffers[filename], filepath, done);
         }, actionDone);
@@ -40,13 +40,13 @@ exports = module.exports = function update(globals, state, next) {
             return actionDone(null);
         }
 
-        async.each(state.diffs.deleted, function(filename, done) {
+        async.eachSeries(state.diffs.deleted, function(filename, done) {
             var filepath = path.join(state.remotedir.path, filename);
             globals.ftp.raw.dele(filepath, done);
         }, actionDone);
     }
 
-    async.parallel([
+    async.series([
         push,
         del,
     ], function(actionErr) {