api.py is available since
0.8.0 and above (latest version is
1.7.1), see here.
You can find your version using..
To update, since your install is located in the Maya lib directory, I would suggest..
$ cd c:\program files\autodesk\maya2018\python\lib\site-packages
$ pip install pyblish-qml --update --target .
--target . argument will install it into the local directory, and should replace your current install. If not, then try first removing your existing install. You may also need to run the command-line as Administrator, since that directory is likely write-protected.
Alternatively, you can download the zip from the GitHub link above.