wrong package name

.travis.yml

@@ -9,7 +9,7 @@ before_install:
   - sudo apt-get update -qq
   - if [ "$CXX" = "g++" ]; then sudo apt-get install -qq g++-4.8; fi
   - if [ "$CXX" = "g++" ]; then export CXX="g++-4.8" CC="gcc-4.8"; fi
-  - sudo pip install cpp-coveralls yaml
+  - sudo pip install cpp-coveralls pyyaml
 
 before_script:
   - autoreconf -iv