Build libyaml on travis

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 603ee94..55bb497 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -21,6 +21,20 @@
     - python: pypy
       env: TOXENV=pypy
 
+# build libyaml
+before_script:
+- >-
+  cd /tmp
+  && git clone https://github.com/yaml/libyaml.git -b 0.2.2-pre1 libyaml
+  && cd libyaml
+  && ./bootstrap
+  && ./configure
+  && make
+  && make test-all
+  && sudo make install
+  && sudo ldconfig
+  && cd "$TRAVIS_BUILD_DIR"
+
 install: pip install cython tox
 
 script: tox