Change from GPL3+ to MIT license. Closes #81 (#86)

Author: molpopgen

Cargo.toml

@@ -4,7 +4,7 @@ version = "0.1.3"
 authors = ["molpopgen <[email protected]>"]
 edition = "2018"
 description = "Tools for forward simulation with tree sequence recording"
-license = "GPL-3.0-or-later"
+license = "MIT"
 homepage = "https://github.com/ForwardSimulation/forrustts"
 repository = "https://github.com/ForwardSimulation/forrustts"
 keywords = ["simulation", "tree_sequences", "tskit", "population_genetics"]