Fix Incorrect Entity Spans

[BorisPolonsky]

Fix Incorrect Entity Spans

Brief

Fixed inconsistency in span definition between

• entities located in the beginning of a sentence (fixed)
• the rest that follows the definition of Rasa NLU JSON format (left as is).

Entities are specified with a start and an end value, which together make a python style range to apply to the string, e.g. in the example below, with text="show me chinese restaurants", then text[8:15] == 'chinese'.

[howl-anderson]

@BorisPolonsky Thank you for your PR. I am sorry for the delay. I am recently very busy, I will take a close look as soon as possible. I will keep you informed!