travis.ci: enable ctest_output_on_failure

gcontini

2020-04-26 b01f4512ae3aa25426cb84758a791478ab68d5d7

 test/library/CMakeLists.txt

@@ -14,7 +14,7 @@
ELSE(WIN32)
    add_executable(
       test_os_linux
       Os_Linux_test.cpp
       os_linux_test.cpp
   )

   target_link_libraries(