added travis

.travis.yml

+sudo: required
+dist: trusty
+before_install:
+- sudo apt-get -qq update && sudo apt-get install -y --no-install-recommends texlive-fonts-recommended texlive-latex-extra texlive-fonts-extra dvipng texlive-latex-recommended
+script:
+- mkdir _build
+- pdflatex -interaction=nonstopmode -halt-on-error -output-directory _build cours.tex
+# deploy:
+#   provider: releases
+#   api_key:
+#     secure: [YOUR KEY]
+#   file:
+#   - _build/cours.pdf
+#   skip_cleanup: true
+#   on:
+#     tags: true