Creating a development environment doesn't work as expected in doc 
Hello,

I need to create a development environment for Pandas ( https://github.com/pandas-dev/pandas/issues/9154#issuecomment-329795314 )

So I try to follow https://pandas.pydata.org/pandas-docs/stable/contributing.html#creating-a-development-environment

```
$ conda create -n pandas_dev python=3 --file ci/requirements_dev.txt
Fetching package metadata .........

PackageNotFoundError: Packages missing in current channels:

  - moto

We have searched for the packages in the following channels:

  - https://repo.continuum.io/pkgs/free/osx-64
  - https://repo.continuum.io/pkgs/free/noarch
  - https://repo.continuum.io/pkgs/r/osx-64
  - https://repo.continuum.io/pkgs/r/noarch
  - https://repo.continuum.io/pkgs/pro/osx-64
  - https://repo.continuum.io/pkgs/pro/noarch
```

Pinging @jorisvandenbossche 