update texlive in travis-ci to 2017-07-05 (#143)

* fix travis ci

* fix missing path

* update texlive to 2017-09-18

.travis.yml

@@ -1,12 +1,9 @@
 before_install:
-   - sudo add-apt-repository -y ppa:texlive-backports/ppa
    - sudo apt-get update
 install:
-   - sudo apt-get install -y texlive-latex-base 
-   - sudo apt-get install -y texlive-latex-recommended texlive-latex-extra
-   - sudo apt-get install -y texlive-science 
-   - sudo apt-get install -y texlive-fonts-recommended texlive-fonts-extra
-   - sudo apt-get install -y psutils
+   - sudo apt-get install ghostscript
+   - curl -L https://github.com/holgern/travis-texlive/releases/download/2017-09-18_02/texlive.tar.xz | tar -JxC ~
+   - PATH=$HOME/texlive/bin/x86_64-linux:$PATH
 script:
    - make clean
    - make BUILD_STRATEGY=latex