add missing test dependency to libsubunit

Author: satta

.travis.yml

@@ -4,5 +4,5 @@ compiler:
   - clang
 before_install:
  - sudo apt-get update -qq
- - sudo apt-get install -qq check
+ - sudo apt-get install -qq check libsubunit0-dev
 script: autoreconf -i && ./configure && make && make check