Merge pull request #129 from RiveraGroup/bugfix/mongo_2.6.5_project_doc_source

Creation technique of ObjectExpression is incorrect

lib/pipeline/documentSources/ProjectDocumentSource.js

@@ -13,7 +13,7 @@ var DocumentSource = require('./DocumentSource');
 var ProjectDocumentSource = module.exports = function ProjectDocumentSource(ctx){
 	if (arguments.length > 1) throw new Error("up to one arg expected");
 	base.call(this, ctx);
-	this.OE = new ObjectExpression();
+	this.OE = ObjectExpression.create();
 	this._raw = undefined;
 }, klass = ProjectDocumentSource, base = require('./DocumentSource'), proto = klass.prototype = Object.create(base.prototype, {constructor:{value:klass}});