Tests are running sequentially in protractor even when shard files is true

I am running the tests using protractor .I have 3 specs file but still it runs sequentially What am i missing here ? Code : capabilities: { 'browserName': 'chrome', chromeOptions: { args: ['--headless', "--disable-gpu", "--window-size=1920,1080"]

    },
    // Ability to run the tests in parallel.
    shardTestFiles: true,
    maxInstances: 2
},