Small adjustment on sign_out function (#603)

* Small adjustment on sing_out function

First, thanks for this. It has been a great help. I was having trouble with this function, getting a TypeError (TypeError: can only concatenate str (not "NoneType") to str) because apparently the second os.remove(session_cache_path()) is trying to delete a file that does not exist anymore so this is what worked for me.

* Change description on app.py file

* Update app.py on line 79

Fixed indent

examples/app.py

@@ -73,11 +73,10 @@ def index():
 
 @app.route('/sign_out')
 def sign_out():
-    os.remove(session_cache_path())
-    session.clear()
     try:
         # Remove the CACHE file (.cache-test) so that a new user can authorize.
         os.remove(session_cache_path())
+        session.clear()
     except OSError as e:
         print ("Error: %s - %s." % (e.filename, e.strerror))
     return redirect('/')