[Enhancement/Bug Fix] Tiingo Backend Uses JSON Which Conflicts With Python Boolean Calls

* Tiingo Python version: 0.13
* Python version: 3.8.8
* Operating System: Windows/Ubuntu 18.04

### Description

Made a call to IEX Intraday data enabling the "&afterHours=True" parameter. The problem is with the Pythonic need for True and False to be capitalized which conflicts with JSONs need to use "true" and "false" lowercase.

I expected the API call to return fruitful but instead returned None.

### What I Did

I suggest that we utilize a JSON.dump(url_parameters) going forward to be better able to adapt to changes in the Tiingo API. A simple function could be created that is called before returning the URL string to the requests library.

Please see an excerpt from an email exchange from @tiingo:

> Interesting little 'bug' or 'feature': When getting intraday IEX quotes and choosing afterHours=true or afterHours=false the boolean MUST BE lowercase which is an interesting little incompatibility with Python that likes Booleans to be either True or False. So, I can workaround with using an encapsulated 'true' or 'false' but as you continue making your API v2, this might be something worth examining.

@tiingo response:

> This behavior is intentional

> REST APIs typically take data in JSON format - the lowercase true/false is a function of following this spec (JSON booleans are lowercase).

> In the backend, the json is parsed into Python using a standard json parsing library.

> This is a function of following standard web practices - if you want to send a request to the API, you could use a standard json encoding library (ujson, simplejson for example). then do json.dumps(pythonObj) to get the JSON representation

I believe it's only a matter of time, as in my attempted enhancement, before the V2 API or later functionality exposes this "bug" in the code.