It's zipped to reduce file size. You have to unzip the file first, you should be able to install the apk-file inside the folder. Sorry, if that wasn't clear enough, I'm going to add a description to the download. Just give me a note, if there are any further problems.
If your phone doesn't already have a file manager installed, you can get the app 'Files by google' in the playstore, this should be able to open it. To not make things more complicated I have replaced the file with an unzipped one for now, so you just have to download and install it. Hope this works! :3