MAINT: try fixing latex doc build error

matthew-brett · matthew-brett · commit b27b1e280078 · 2018-01-15T14:37:00.000Z
Install missing package.
diff --git a/.travis.yml b/.travis.yml
@@ -80,6 +80,7 @@ matrix:
             - texlive-latex-extra
             - texlive-fonts-recommended
             - texlive-latex-recommended
+            - latexmk
 
 before_install:
     - source tools/travis_tools.sh
