add building the hvl library to the test cases

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index cbd3f12..d49af66 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -33,6 +33,8 @@
       env: STD_CELL_LIBRARY=sky130_fd_sc_ls
     - name: "hdll library"
       env: STD_CELL_LIBRARY=sky130_fd_sc_hdll
+    - name: "hvl library"
+      env: STD_CELL_LIBRARY=sky130_fd_sc_hvl
     - name: "all libraries"
       env: STD_CELL_LIBRARY=all
   allow_failures:

.travisCI/Makefile

diff --git a/.travisCI/Makefile b/.travisCI/Makefile
index 5d0140a..d6bb932 100644
--- a/.travisCI/Makefile
+++ b/.travisCI/Makefile
@@ -49,6 +49,7 @@
 		git submodule update --init libraries/sky130_fd_sc_hdll/latest && \
 		git submodule update --init libraries/sky130_fd_sc_ms/latest && \
 		git submodule update --init libraries/sky130_fd_sc_ls/latest && \
+		git submodule update --init libraries/sky130_fd_sc_hvl/latest && \
 		$(MAKE) -j$(THREADS) timing
 
 .PHONY: build-pdk