Travis CI does not provide valgrind by default

.travis.yml

@@ -1,6 +1,8 @@
 language: c
 compiler:
   - gcc
+before_install:
+  - sudo apt-get install cmake valgrind
 script:
   - mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Debug .. && make && ./test-xml && valgrind --tool=memcheck --leak-check=full --track-origins=yes -v ./test-xml