Adding -j flag to make to accelerate build

Using a conditional || so that non-interleaved error information can be presented if there are compilation problems

.travis.yml

@@ -27,7 +27,7 @@ before_script:
 script:
   - export CPATH=/usr/include/c++/4.8:/usr/include/x86_64-linux-gnu/c++/4.8/:$CPATH
   - export LD_LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.8:$LD_LIBRARY_PATH
-  - make
+  - make -j 16 || make
   - make test
 os:
   - linux