Adapting code to python-telegram-bot 8.1.1

[lucaspg96]

There were only 2 problems on the lib:

• First, the Mockbot must to have a "request" attribute. The value is an object telegram.util.request.Request;
• Second, the User constructor from telegram.User needs a new argument: is_bot. This values defines if the user is a bot or not. When using inside the Mockbot, I set this value to True. On the usergenerator class, I added this variable and set as default False.

I don't know exactly how Travis works, but, to execute the tests here, I need to change the system path on each test class. I made this modifications, but you can change if necessary.

If is everything ok, can you release this lib? I need it on a application that I'm building.

[codecov]

Codecov Report

Merging #17 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #17      +/-   ##
==========================================
+ Coverage   99.68%   99.68%   +<.01%     
==========================================
  Files          11       11              
  Lines         939      941       +2     
==========================================
+ Hits          936      938       +2     
  Misses          3        3

Impacted Files	Coverage Δ
ptbtest/usergenerator.py	100% <ø> (ø)	⬆️
ptbtest/mockbot.py	99.48% <100%> (ø)	⬆️

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[Bibo-Joshi]

Hi. I'm notifying everyone who PRed to this repo about #21.