create_all() failing.

[zengoma]

Hi
I recently pushed all my static assets to s3 and set up cloudfront CDN successfully. Afterwards I realized that I forgot to set a Cache-Control header. I also added some additional assets. I'm receiving the following traceback error when running create_all() function:

Traceback (most recent call last):
  File "app/upload_assets.py", line 6, in <module>
    flask_s3.create_all(app)
  File "C:\projects\adminout\venv\lib\site-packages\flask_s3.py", line 453, in create_all
    _upload_files(s3, app, all_files, bucket_name)
  File "C:\projects\adminout\venv\lib\site-packages\flask_s3.py", line 318, in _upload_files
    names, bucket, hashes=hashes))
  File "C:\projects\adminout\venv\lib\site-packages\flask_s3.py", line 289, in _write_files
    merged_dicts = merge_two_dicts(get_setting('FLASKS3_HEADERS', app), h)
  File "C:\projects\adminout\venv\lib\site-packages\flask_s3.py", line 82, in merge_two_dicts
    z = x.copy()
AttributeError: 'tuple' object has no attribute 'copy'

My relevant app config:

...
    FLASKS3_BUCKET_NAME = 'mybucket'
    FLASKS3_GZIP = True
    FLASK_ASSETS_USE_S3 = True
    FLASK_ASSETS_USE_CDN = True
    FLASKS3_REGION = 'ap-south-1'
    FLASKS3_BUCKET_DOMAIN = u's3.ap-south-1.amazonaws.com'
    FLASKS3_CDN_DOMAIN = u'mycdn.cloudfront.net'
    FLASKS3_HEADERS = {
        'Cache-Control': 'max-age=84600'
    }
...

I am running the following python script to update my assets:

"""
Script for uploading latest assets to S3 bucket
"""
import flask_s3
from main import app
flask_s3.create_all(app)

My environment: Windows 10, Python 3.6.1 virtualenv.
Is this an issue or have I done something stupid? Please help!