Add versions to build dependencies

python/MANIFEST.in

@@ -2,6 +2,7 @@ include stan/unix/*.stan
 include stan/win/*.stan
 include LICENSE
 include requirements.txt
+include pyproject.toml
 
 # Ensure in-place built models do not get included in the source dist.
 prune fbprophet/stan_model

python/pyproject.toml

@@ -1,2 +1,2 @@
 [build-system]
-requires = ["cython", "numpy", "pystan"]
+requires = ["Cython>=0.22", "numpy>=1.10.0", "pystan>=2.14"]