Show clang version in Travis build.

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 558702d..87e777a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -43,6 +43,7 @@
   - ${CXX} ${EXTRA_CXXFLAGS} -std=c++11 -Wall -g -o loader_example loader_example.cc
   - ./loader_example ./models/Cube/Cube.gltf
   - cd tests
+  - clang++ -v
   - make
   - ./tester
   - ./tester_noexcept