The plugin listens for the double click on the content and then tries to check first the boundaries of the selection that the browser has created, so it tries to select only a text node and after that if the end of the selection is a space just moves it one place back.
The recommended way to install all CKEditor add-ons is to create a custom build by using Online builder. To do that, click the Add to my editor button on the plugin page. When you are done, click the Build my editor button on the right side of the page to go to Online builder.
Note: This add-on is already selected to be a part of your current build.
Add-on installation instructions
If you want to add the plugin manually, you will need to:
Extract the downloaded plugin .zip into the plugins folder of your CKEditor installation. Example: