use komake for safer parallel builds
diff --git a/misc/docker-ci.mk b/misc/docker-ci.mk
index 9c543f0..aa872cf 100644
--- a/misc/docker-ci.mk
+++ b/misc/docker-ci.mk
@@ -19,5 +19,5 @@
 
 _do-check:
 	cmake $(CMAKE_ARGS) "-H$(SRC_DIR)" -B.
-	make all VERBOSE=1
+	komake -j4 all VERBOSE=1
 	env $(CHECK_ENVS) make check