• I am on the latest Poetry version.
• I have searched the issues of this repo and believe that this is not a duplicate.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: MacOS
• Poetry version: Poetry 0.11.5

Issue

My app is depending on the wsproto library. wsproto itself is depending on h11 >=0.7.0,<0.8.0.
It happens that h11 has a bug which I fixed; the h11 project has merged this but not yet published an update.

I'd like to therefore install the master branch of h11. I am doing this:

poetry add wsproto
poetry add --git https://github.com/miracle2k/h11.git h11

However, it seems that my "git overrride" is ignored:

$ poetry show
atomicwrites   1.2.1  Atomic file writes.
attrs          18.2.0 Classes Without Boilerplate
h11            0.7.0  A pure-Python, bring-your-own-I/O implementation of HTTP/1.1
more-itertools 4.3.0  More routines for operating on iterables, beyond itertools
pluggy         0.7.1  plugin and hook calling mechanisms for python
py             1.6.0  library with cross-python path, ini-parsing, io, code, log facilities
pytest         3.8.0  pytest: simple powerful testing with Python
six            1.11.0 Python 2 and 3 compatibility utilities
wsproto        0.11.0 WebSockets state-machine based protocol implementation

$ poetry run  pip freeze
atomicwrites==1.2.1
attrs==18.2.0
h11==0.7.0
more-itertools==4.3.0
pluggy==0.7.1
py==1.6.0
pytest==3.8.0
six==1.11.0
wsproto==0.11.0

If I poetry remove wsproto, it installs the correct git dependency and shows as the version h11==0.8.1+dev.

At the very least, I would expect here to be conflict: if wsproto requires a version <0.8, but I require a specific git install with a version >0.8, this should be unresolvable.

Ideally, I'd like a way to to ignore the overlay restrictive wsproto version range and install the version I tell it to.