I had a quick look around, as you did, but I couldn't find a chart which included the Libertarian Party. Nevertheless, we can use data from the Cooperative Congressional Election Study 2018 to produce one. After weighting the raw data to be representative of the registered voter population, we are left with a dataset which provides education data for just over 10,000 Democrats, around 8,000 Republicans, and 130 Libertarians, as validated by Catalist. It is up to the reader whether this is a large enough sample on the Libertarian side of things for this data to be meaningful.
Using this data, we can produce the following chart, indicating the percentage of individuals registered to each party at that level of education.