Raise support for oldest support

Author: mobiusklein

pyproject.toml

@@ -2,7 +2,7 @@
 requires = ["setuptools",
             "wheel",
             "Cython",
-            "oldest-supported-numpy; python_version >= '3.7'",
+            "oldest-supported-numpy; python_version >= '3.8'",
             "numpy==1.16.1; python_version <= '3.7' and python_version >= '3'",
             "numpy==1.13.3; python_version=='2.7'",
             "brain-isotopic-distribution",