Allow flask 1.x, match runserver.py code to tutorial

Author: Kraig Brockschmidt

requirements.txt

@@ -1 +1 @@
-Flask<1
+flask

runserver.py

@@ -1,11 +1,11 @@
-import os
+from os import environ
 from HelloFlask import app
 
 if __name__ == '__main__':
-    HOST = os.environ.get('SERVER_HOST', 'localhost')
+    HOST = environ.get('SERVER_HOST', 'localhost')
 
     try:
-        PORT = int(os.environ.get('SERVER_PORT', '5555'))
+        PORT = int(environ.get('SERVER_PORT', '5555'))
     except ValueError:
         PORT = 5555