style: Fix flake8 complaints

Remove unused imports in main.py

Add missing "global" in webserver and fix spacing.

Signed-off-by: Matthias Blankertz <matthias@blankertz.org>

software/src/main.py

@@ -9,9 +9,7 @@ import micropython
 import network
 import os
 import time
-from math import pi, sin, pow
 import ubinascii
-from microdot import Microdot
 
 # Own modules
 import app

software/src/webserver.py

@@ -10,9 +10,12 @@ from microdot import Microdot
 webapp = Microdot()
 server = None
 
+
 def start_webserver():
+    global server
     server = asyncio.create_task(webapp.start_server(port=80))
 
+
 @webapp.route('/')
 async def index(request):
     print("wohoo, a guest :)")