allennlp requires conflicting dependencies: cffi (1.11.2) != (>=1.11.5)

[diefans]

Describe the bug

allennlp directly requires cffi (1.11.2)
allennlp directly requires gevent (1.3.5) which requires cffi (>=1.11.5)

So you end up with cffi (1.11.2) != (>=1.11.5)

I use poetry to keep my dependencies locked:

[SolverProblemError]
Because allennlp (0.6.1) depends on gevent (1.3.5) which depends on cffi (>=1.11.5), allennlp (0.6.1) requires cffi
 (>=1.11.5).
And because allennlp (0.6.1) depends on cffi (1.11.2), allennlp is forbidden.
So, because no versions of allennlp match >0.6.1,<0.7.0
 and questionanswering-service depends on allennlp (^0.6.1), version solving failed.

A clear and concise description of what the bug is.

To Reproduce
poetry add allennlp

Expected behavior
Installable allennlp.

System (please complete the following information):

• OS: Ubntu 16.04
• Python version: 3.6.6
• AllenNLP version: v0.6.1

[schmmd]

@diefans thanks for reporting. I'm unfamiliar with poetry. Do you have a pyproject.toml file for allennlp? Here's what I get when I run you command:

poetry add allennlp                                                                         
[RuntimeError]                                                                          
Poetry could not find a pyproject.toml file in /Users/michaels/hack/allenai/allennlp or its parents  

[schmmd]

Fixes #1846

[phiresky]

this issue still happens (or happens again) with allennlp v0.7.2

[SolverProblemError]                                                  
Because gevent (1.3.6) depends on cffi (>=1.11.5)                                  
 and allennlp (0.7.2) depends on cffi (1.11.2), gevent (1.3.6) is incompatible wi  
th allennlp (0.7.2).                                                               
And because allennlp (0.7.2) depends on gevent (1.3.6), allennlp is forbidden.     
So, because no versions of allennlp match >0.7.2,<0.8.0                            
 and code depends on allennlp (^0.7.2), version solving failed.