fix typo in explanation of keystroke explanationn

fix typo

Previous instructions fail due trying to use CRAN without setting a mirror.

Close swcarpentry/lesson-example#208

Add notes about style for emphasis and span of code

As suggested by @gcapes.

v9.5.0

New Features

- Migrate `bin/*.py` to Python 3

  Because Python 2 will not be supported soon
  and we are teaching Python 3 for a while.
- Add note about the version of the style

  This will help maintainers, contributors and users.
- Move boilerplate files to their own file

  This will help maintainers to copy some files.
- Add `.travis.yml`

  This will help contributors to know what is wrong.

Changes

- Fix favicon
- Fix search (powered by Google)
- Clean footer HTML
- Fix Copyright information
- Fix line wrap after dash in code block
- Fix font size of h2 in call out box
- Remove root and layout from YAML for boilerplate
- Make Jekyll ignore .Rproj

Contributors

- Andy Boughton (@abought)
- François Michonneau (@fmichonneau)
- Joseph Stachelek (@jsta)
- Katrin Leinweber (@katrinleinweber)
- Maxim Belkin (@maxim-belkin)
- Michael R. Crusoe (@mr-c)

Fix lesson_check.py

Run lesson-fixme from within lesson-check

Change shebang to Python3

Close swcarpentry/styles#271

Make Jekyll ignore .Rproj

Port of https://github.com/swcarpentry/r-novice-inflammation/commit/9da857efb16d7351127f2d5c46fc0af660654506.

Close swcarpentry/styles#274

Improve .travis.yml to build the lesson

Add Travis CI file

Remove root and layout from YAML for boilerplate

Remove root and page from YAML header

Close swcarpentry/lesson-example#205

Remove unnecessary super call

Use Python3-style class declaration

util.py: make functions return NotImplemented

R package stringer to stringr

missing comma in boilerplate generation

lesson_check: fix create_checker function