NO-JIRA Perform Travis compilation in parallel (#206)

diff --git a/.travis.yml b/.travis.yml
index 83cc98d..c6828a7 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -83,5 +83,5 @@
 - cmake .. -DCMAKE_INSTALL_PREFIX=$PWD/install ${QPID_PROTON_CMAKE_ARGS}
 
 script:
-- cmake --build . --target install && ctest -V ${QPID_PROTON_CTEST_ARGS}
+- cmake --build . --target install -- -j$(nproc) && ctest -V ${QPID_PROTON_CTEST_ARGS}