404 not found [IP:91.189.95.83] while sudo add-apt-repository -y ppa:pmiller-opensource/ppa

Hi，

I met an error while I run
`sudo add-apt-repository -y ppa:pmiller-opensource/ppa`

I want to install the microbit-micropython on ubuntu 18.04.1 LTS

Here is the error report:

```
Ign:1 http://mirrors.aliyun.com/ubuntu trusty InRelease
Hit:2 http://mirrors.aliyun.com/ubuntu trusty-security InRelease
Hit:3 http://mirrors.aliyun.com/ubuntu trusty-updates InRelease
Hit:4 http://mirrors.aliyun.com/ubuntu trusty-proposed InRelease
Ign:5 http://ppa.launchpad.net/pmiller-opensource/ppa/ubuntu bionic InRelease
Hit:6 http://mirrors.aliyun.com/ubuntu trusty-backports InRelease
Hit:7 http://mirrors.aliyun.com/ubuntu trusty Release
Hit:9 http://ppa.launchpad.net/team-gcc-arm-embedded/ppa/ubuntu bionic InRelease
Err:10 http://ppa.launchpad.net/pmiller-opensource/ppa/ubuntu bionic Release
404 Not Found [IP: 91.189.95.83 80]
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/pmiller-opensource/ppa/ubuntu bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
```

Is there anyway to fix this?