Fix presumed typo

I assume a trailing slash should be removed

realms/config/__init__.py

@@ -178,7 +178,7 @@ LOGIN_DISABLED = ALLOW_ANON
 LOCKED = WIKI_LOCKED_PAGES[:]
 
 if BASE_URL.endswith('/'):
-    BASE_URL = BASE_URL[-1]
+    BASE_URL = BASE_URL[:-1]
 
 SQLALCHEMY_DATABASE_URI = DB_URI