Set minimum Python version to 3.8

The Numpy version is pinned to 1.22 in the conda-forge configuration. This version of Numpy requires at least Python 3.8 per the Numpy docs (https://numpy.org/devdocs/release/1.22.0-notes.html#python-3-7-is-no-longer-supported).

Author: rafmudaf

setup.py

@@ -35,7 +35,7 @@
 URL = 'https://github.com/NREL/ROSCO'
 EMAIL = 'daniel.zalkind@nrel.gov'
 AUTHOR = 'NREL, National Wind Technology Center'
-REQUIRES_PYTHON = '>=3.4'
+REQUIRES_PYTHON = '>=3.8'
 VERSION = '2.7.0'
 
 # These packages are required for all of the code to be executed.