THRIFT-3690 Work around docker image build failures on Travis-CI
Client: Build
Patch: Nobuaki Sukegawa

This closes #906
diff --git a/build/docker/scripts/cmake.sh b/build/docker/scripts/cmake.sh
index 8204a1d..0b92c5b 100755
--- a/build/docker/scripts/cmake.sh
+++ b/build/docker/scripts/cmake.sh
@@ -3,6 +3,6 @@
 
 mkdir -p cmake_build && cd cmake_build
 cmake $* ..
-make -j4
+make -j3
 cpack
 ctest -VV -E "(concurrency_test|processor_test)"