BLD: Install texlive packages in Travis CI

- Closes #12543  - `texlive-latex-base` needed for `latex`  -
`texlive-latex-extra` needed for `utf8x.def`

Author: Alex Alekseyev <[email protected]>

Closes #12544 from evectant/issue-12543 and squashes the following commits:

c95c361 [Alex Alekseyev] BLD: Install texlive packages in Travis CI

Author: Alex Alekseyev

ci/build_docs.sh

@@ -19,7 +19,7 @@ if [ x"$DOC_BUILD" != x"" ]; then
     source activate pandas
     conda install -n pandas -c r r rpy2 --yes
 
-    time sudo apt-get $APT_ARGS install dvipng
+    time sudo apt-get $APT_ARGS install dvipng texlive-latex-base texlive-latex-extra
 
     mv "$TRAVIS_BUILD_DIR"/doc /tmp
     cd /tmp/doc