try to clean up coverage and fix coveralls->github link

.travis.yml

@@ -35,5 +35,8 @@ after_success:
  - |
    if [[ "${COVERAGE}" == "ON" ]]; then
      lcov --directory source/CMakeFiles/xlnt.dir --capture --output-file coverage.info --base-directory ../source --no-external --gcov-tool /usr/bin/gcov-6
+     lcov --remove coverage.info source/detail/miniz.cpp
+     i=$(dirname $(pwd))
+     sed -i "s|$i/||" coverage.info
      coveralls-lcov coverage.info
    fi