Use CIRCLE_PROJECT_REPONAME to reference local repo

[nethsix]

Previously we used a fixed name, e.g., ruby-tensorflow as local repo name but this turns out to be tensorflow.rb for some people, so we use CIRCLE_PROJECT_REPONAME

[nethsix]

@Arafatk Apparently I cloned your repo using the url https://github.com/Arafatk/ruby-tensorflow while others used https://github.com/Arafatk/tensorflow.rb. Thus I had always thought that the code will be cloned into ruby-tensorflow directory but that is not the case for others. Thus I am using CIRCLE_PROJECT_REPONAME instead of hard-coding ruby-tensorflow in the script.

[arafatkatze]

@nethsix Thanks.