Fix write option.

setup.py

@@ -59,7 +59,7 @@ def setup_etherpad():
     data = f.read()
     f.close()
     data.replace('#ETHERPAD_URL_BASE=http://etherpad.meet.jitsi:9001', 'ETHERPAD_URL_BASE=http://etherpad:9001')
-    f = open('.env', w)
+    f = open('.env', 'w')
     f.write(data)
     f.close()