update filename_format ProfilerMiddleware

[lidayan]

there is a error when formating string(default-file-name), like this:

Traceback (most recent call last):
  File "werkzeug/middleware/profiler.py", line 119, in __call__
    time=time.time()
ValueError: Unknown format code 'd' for object of type 'float'

fixes #1511

[davidism]

I messed up and didn't notice that you'd committed to your master branch. Try to avoid doing that, as any pushes I make as maintainer will mess up your repo. You'll want to delete your fork and recreate it if you want to contribute again.

I'll create a separate PR with your commits, so you'll still get the credit for this.