Do not crash if app.volumes does not exist

src/docker.js

@@ -190,7 +190,7 @@ function getBinds(app, callback) {
     assert.strictEqual(typeof app, 'object');
     assert.strictEqual(typeof callback, 'function');
 
-    if (app.volumes.length === 0) return callback(null);
+    if (!app.volumes || app.volumes.length === 0) return callback(null);
 
     let binds = [];