"The Construct Classic editor is licensed under the GPL 2.0."
As Ashley says, the editor is GPL, and games maded with it is BSD-licensed.
"However, the runtime is BSD-licensed as of 17th August 2011 (formerly it was also GPL). This means the games you make in Classic are not touched by the GPL license. "
"In short: you can make commercial games, royalty-free, in Construct Classic."