Strange pip freeze entry for promise library

[FrankSalad]

Hello
I got an entry in the output of pip freeze of promise==2.1.dev0 when I ran the command pip install "graphene-django>=2.0.dev" as instructed on the graphene-django README. The output of the installation:

 pip install "graphene>=2.0.dev"
Collecting graphene>=2.0.dev
  Downloading graphene-2.0.dev20170802065539-py2.py3-none-any.whl (101kB)
    100% |████████████████████████████████| 102kB 2.9MB/s 
Collecting promise>=2.1.dev (from graphene>=2.0.dev)
  Downloading promise-2.1.dev20170724043809.tar.gz
Collecting graphql-relay>=0.4.5 (from graphene>=2.0.dev)
  Downloading graphql-relay-0.4.5.tar.gz
Requirement already satisfied: six>=1.10.0 in /usr/local/lib/python2.7/site-packages (from graphene>=2.0.dev)
Collecting graphql-core>=2.0.dev (from graphene>=2.0.dev)
  Downloading graphql_core-2.0.dev20171009101843-py2.py3-none-any.whl (198kB)
    100% |████████████████████████████████| 204kB 4.4MB/s 
Collecting typing (from promise>=2.1.dev->graphene>=2.0.dev)
  Downloading typing-3.6.2-py2-none-any.whl
Building wheels for collected packages: promise, graphql-relay
  Running setup.py bdist_wheel for promise ... done
  Stored in directory: /root/.cache/pip/wheels/0c/34/5d/d5ac33be1c9f2c28dca915e532c700449db8de3f2290dc668d
  Running setup.py bdist_wheel for graphql-relay ... done
  Stored in directory: /root/.cache/pip/wheels/36/48/a7/94970107c36122aabf3112e850fb3aae0d2c0cc7882445e152
Successfully built promise graphql-relay
Installing collected packages: typing, promise, graphql-core, graphql-relay, graphene
Successfully installed graphene-2.0.dev20170802065539 graphql-core-2.0.dev20171009101843 graphql-relay-0.4.5 promise-2.1.dev0 typing-3.6.2

When I later inflated the requirements inside a docker environment, pip failed with an error:

Collecting promise==2.1.dev0 (from -r requirements.txt (line 89))
  Could not find a version that satisfies the requirement promise==2.1.dev0 (from -r requirements.txt (line 89)) (from versions: 0.1.0, 0.2.0, 0.2.1, 0.2.2, 0.4, 0.4.1, 0.4.2, 0.4.3, 1.0.0, 1.0.1, 2.0.dev20170313081902, 2.0.dev20170313082331, 2.0.dev20170314074715, 2.0.dev20170317055346, 2.0b1, 2.0rc1, 2.0rc2, 2.0, 2.0.1, 2.0.2, 2.1.dev20170724043809)
No matching distribution found for promise==2.1.dev0 (from -r requirements.txt (line 89))

I replaced the line with promise==2.1.dev20170724043809 and pip completed successfully, but issued a warning when it went to install the library:

Collecting promise==2.1.dev20170724043809 (from -r requirements.txt (line 89))
  Downloading promise-2.1.dev20170724043809.tar.gz
  Requested promise==2.1.dev20170724043809 from https://pypi.python.org/packages/42/2b/36a50e483ad73b59b1851b0601cdac4b6a1a48a9f3940c3851930a5538fa/promise-2.1.dev20170724043809.tar.gz#md5=6a92f0a95e9b980b0415be99c3c9bb4e (from -r requirements.txt (line 89)), but installing version None

My pip version is 9.0.1
Is this something I can safely ignore?

Thanks!