Merge pull request #933 from embark-framework/fix_contracts_json

output contracts json even if the pipeline is empty

lib/pipeline/pipeline.js

@@ -26,7 +26,7 @@ class Pipeline {
     let placeholderPage;
 
     if (!this.assetFiles || !Object.keys(this.assetFiles).length) {
-      return callback();
+      return self.buildContracts(callback);
     }
 
     async.waterfall([