*.ipynb: Use absolute URLs to link to the glossary

*.ipynb: Use absolute URLs to link to the glossary

SWC has a single, global glossary [1], not per-subject glossaries.
Because this per-subject branch no longer contains the global
glossary, we need to adjust the links to point at an external
glossary.  Done automatically with:

  $ sed -i 's|\.\./\.\./gloss.html|https://github.com/swcarpentry/bc/blob/ma
ster/gloss.md|g' *.md

[1]: https://github.com/swcarpentry/bc/blob/master/gloss.md