prepare automated builds for python 3.7

Author: Roberto De Ioris

tools/release_win64.py

@@ -6,7 +6,7 @@
 import zipfile
 
 UE_VERSIONS = ['4.15', '4.16', '4.17', '4.18', '4.19']
-PYTHON_VERSIONS = ["C:/Program Files/Python36", "C:/Python27"]
+PYTHON_VERSIONS = ["C:/Program Files/Python36", "C:/Program Files/Python37", "C:/Python27"]
 
 RELEASE_DIR = sys.argv[1].rstrip('/')