* Maplotlib is an important package. It has now its own test checking that a plot can be generated and exported has an image.
* Some helpers methods added to the `Makefile` mainly permitting to clean containers and images
* Improved assertion messages of some tests

add pytables and bottleneck

[DOC] Selecting image doc minor fixes

* Fix a sentence saying that `pandoc` is not installed on `base-notebook` #1013
* Precision on emacs installation (`emacs-nox`) #1059

Added basic tests on some important components

add vim to minimal-notebook (cf. issue 779)

[DOC] #1060 Fix conda command to create env

Housekeeping

* tensorflow basic tests following #1002
* pandas basic tests following #1063

`conda env create` is only to create environment from a `YAML` file.  Fixed the command in "Add a Python 3.x environment".

[Reference](https://conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html)

and also make the code more readable.

- Bump root container version
- Bump  packages of
  - scipy-notebook
  - r-notebook
  - datascience-notebook
- add -y flag to jupyter lab commands in scipy-notebook
- Fix a bug in check outdated packages when packages installed through pip

Tring to swithch to the last bionic Travis build environment.
https://docs.travis-ci.com/user/reference/bionic/

Bump miniconda -> 4.8.2

recipe: dask