Update Heroku deploy link in README.md (#761)

README.md

@@ -104,7 +104,7 @@ Go to <http://127.0.0.1:3000/>.
 | AWS[^1]   | [![AWS CloudFormation Launch Stack SVG Button](https://cdn.rawgit.com/buildkite/cloudformation-launch-stack-button-svg/master/launch-stack.svg)](https://console.aws.amazon.com/cloudformation/home?#/stacks/create/review?stackName=doccano&templateURL=https://s3-external-1.amazonaws.com/cf-templates-10vry9l3mp71r-us-east-1/2019290i9t-AppSGl1poo4j8qpq)  |
 | Azure | [![Deploy to Azure](https://azuredeploy.net/deploybutton.svg)](https://portal.azure.com/#create/Microsoft.Template/uri/https%3A%2F%2Fraw.githubusercontent.com%2Fdoccano%2Fdoccano%2Fmaster%2Fazuredeploy.json)  |
 | GCP[^2] | [![GCP Cloud Run PNG Button](https://storage.googleapis.com/gweb-cloudblog-publish/images/run_on_google_cloud.max-300x300.png)](https://console.cloud.google.com/cloudshell/editor?shellonly=true&cloudshell_image=gcr.io/cloudrun/doccano&cloudshell_git_repo=https://github.com/doccano/doccano.git)  |
-| Heroku  | [![Deploy](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy)  |
+| Heroku  | [![Deploy](https://www.herokucdn.com/deploy/button.svg)](https://dashboard.heroku.com/new?template=https%3A%2F%2Fgithub.com%2Fdoccano%2Fdoccano)  |
 
 > [^1]: (1) EC2 KeyPair cannot be created automatically, so make sure you have an existing EC2 KeyPair in one region. Or [create one yourself](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-key-pairs.html#having-ec2-create-your-key-pair). (2) If you want to access doccano via HTTPS in AWS, here is an [instruction](https://github.com/doccano/doccano/wiki/HTTPS-setting-for-doccano-in-AWS).
 > [^2]: Although this is a very cheap option, it is only suitable for very small teams (up to 80 concurrent requests). Read more on [Cloud Run docs](https://cloud.google.com/run/docs/concepts).