cmake is a requirement only if it's not installed

Author: njzjz

setup.py

@@ -20,7 +20,7 @@
     tf_install_dir = imp.find_module('tensorflow', [site_packages_path])[1]
 
 install_requires=['numpy', 'scipy']
-setup_requires=['setuptools_scm', 'scikit-build', 'cmake']
+setup_requires=['setuptools_scm', 'scikit-build']
 
 # add cmake as a build requirement if cmake>3.0 is not installed
 try: