extraneous 'a'  
extraneous 'a'  

in *Build the app*, replace:

`if you want to use the a shorter option` with
`if you want to use the shorter option`
londoncalling/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,thaJeztah/docker.github.io,londoncalling/docker.github.io,docker/docker.github.io,londoncalling/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,londoncalling/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,londoncalling/docker.github.io