Don't be fooled by the name, this application is not written in Go, that is just a random word that they chose for the name. The application was written in HTML and bundled with a webview powered by CEF (probably Electron). Just download the application and execute `strings goterminal | grep chromium` and you will see what I am talking about; again, this has 0% Go code.
EDIT: Here is the list of 720 NPM packages used by this: http://pastebin.com/raw/VhnuuDdX
EDIT2: To rub salt into the wound, this thing is ~620MB of HTML + JS + Electron, that is more or less how an entire Ubuntu installation was six years ago, like really? An entire basic Linux installation could have been included in all this archive and these guys decided to fill it with JavaScript code. Isn't a terminal emulator supposed to be lightweight?