Prevent AttributeError on docker instance

[guruyaya]

Just tried using this blockchain, and got this exception:
Traceback (most recent call last):
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1982, in wsgi_app
response = self.full_dispatch_request()
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1614, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1517, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1612, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1598, in dispatch_request
return self.view_functionsrule.endpoint
File "blockchain.py", line 254, in full_chain
return jsonify(response), 200
File "/usr/local/lib/python3.6/site-packages/flask/json.py", line 251, in jsonify
if current_app.config['JSONIFY_PRETTYPRINT_REGULAR'] and not request.is_xhr:
File "/usr/local/lib/python3.6/site-packages/werkzeug/local.py", line 347, in getattr
return getattr(self._get_current_object(), name)
AttributeError: 'Request' object has no attribute 'is_xhr'

It might be a mismatch between Request module and Flask installed. However, adding this line can help fix this issue, without me playing with things I don't understand in the docker file

[ericstephens]

I've observed this problem as well when running it outside of Docker.