儘管建置成功，為什麼我在 Heroku 上的 Go 應用程式部署成功，但應用程式卻顯示「應用程式錯誤」？

import (
    "log"
    "fmt"
    "net/http"
    "os"

    "github.com/gorilla/mux"
    "github.com/gorilla/context"

    "gopkg.in/paytm/grace.v1"
)

func main() {
    log.Println("$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ CHIT STARTED $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$")
    log.Println("$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$")

    muxRouter := mux.NewRouter()

    muxRouter.HandleFunc("/", Articles)
    http.Handle("/", muxRouter)

    port := os.Getenv("PORT")
    if port == "" {
        port = "9000" // Default port if not specified
    }

    err := grace.Serve(":" + port, context.ClearHandler(http.DefaultServeMux))
    if err != nil {
        log.Println("[ERROR GRACEFUL]", err)
        os.Exit(1)
    }

    os.Exit(0)
}

func Articles(w http.ResponseWriter, r *http.Request) {
    // vars := mux.Vars(r)
    w.WriteHeader(http.StatusOK)
    fmt.Fprintf(w, "Hello")
    // r.Close = true
    // w.Header().Set("Content-Type", "application/json")
    // w.Header().Set("Access-Control-Allow-Origin", "*")

    /*if r.Method == "OPTIONS" {
        w.WriteHeader(http.StatusOK)
        return
    }

    if err := fn(w, r); err != nil {
        log.Println(err)
        apiObject := ConstructAPIError(http.StatusInternalServerError, ErrGeneral, SysMsgErrGeneral, MsgErrGeneral)
        SendAPIObject(w, apiObject)
        return
    }*/
}

-----> Go app detected
-----> Fetching jq... done
-----> Fetching stdlib.sh.v8... done
-----> Checking Godeps/Godeps.json file.
-----> New Go Version, clearing old cache
-----> Installing go1.12.6
-----> Fetching go1.12.6.linux-amd64.tar.gz... done
-----> Running: go install -v -tags heroku ./... 
bitbucket.org/michaelchandrag/chit/pkg
bitbucket.org/michaelchandrag/chit/vendor/github.com/gorilla/context
bitbucket.org/michaelchandrag/chit/vendor/github.com/gorilla/mux
bitbucket.org/michaelchandrag/chit/vendor/gopkg.in/tylerb/graceful.v1
bitbucket.org/michaelchandrag/chit/vendor/gopkg.in/paytm/grace.v1
bitbucket.org/michaelchandrag/chit/pkg/util
bitbucket.org/michaelchandrag/chit

       Installed the following binaries:
            ./bin/chit
-----> Discovering process types
       Procfile declares types -> web
-----> Compressing...
       Done: 7.5M
-----> Launching...
       Released v3
       https://michaelchandrag-project.herokuapp.com/ deployed to Heroku

2:47.954106+00:00 heroku[web.1]: Starting process with command `chit`
2019-07-08T05:02:49.413453+00:00 app[web.1]: 2019/07/08 05:02:49 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ CHIT STARTED $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
2019-07-08T05:02:49.413476+00:00 app[web.1]: 2019/07/08 05:02:49 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
2019-07-08T05:02:49.413647+00:00 app[web.1]: 2019/07/08 05:02:49 starting serve on  :9000
2019-07-08T05:03:48.131507+00:00 heroku[web.1]: Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch
2019-07-08T05:03:48.131595+00:00 heroku[web.1]: Stopping process with SIGKILL
2019-07-08T05:03:48.214979+00:00 heroku[web.1]: State changed from starting to crashed
2019-07-08T05:03:48.193205+00:00 heroku[web.1]: Process exited with status 137
2019-07-08T10:38:59.721224+00:00 heroku[web.1]: State changed from crashed to starting
2019-07-08T10:39:00.359017+00:00 heroku[web.1]: Starting process with command `chit`
2019-07-08T10:39:02.232435+00:00 app[web.1]: 2019/07/08 10:39:02 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ CHIT STARTED $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
2019-07-08T10:39:02.232458+00:00 app[web.1]: 2019/07/08 10:39:02 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
2019-07-08T10:39:02.232583+00:00 app[web.1]: 2019/07/08 10:39:02 starting serve on  :9000
2019-07-08T10:40:00.462841+00:00 heroku[web.1]: Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch
2019-07-08T10:40:00.462974+00:00 heroku[web.1]: Stopping process with SIGKILL
2019-07-08T10:40:00.555959+00:00 heroku[web.1]: Process exited with status 137
2019-07-08T10:40:00.573427+00:00 heroku[web.1]: State changed from starting to crashed

2019-07-08T05:03:48.131507+00:00 heroku[web.1]: Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch