use GSUTIL variable instead of hardcoded gsutil

Change-Id: If52a1168a3d74ab821dd1838a6c88ef2e47ee928
diff --git a/linux-x86_64/kythe/studio/build_studio_kythe.sh b/linux-x86_64/kythe/studio/build_studio_kythe.sh
index 950ccf1..1d3e662 100755
--- a/linux-x86_64/kythe/studio/build_studio_kythe.sh
+++ b/linux-x86_64/kythe/studio/build_studio_kythe.sh
@@ -57,7 +57,7 @@
 
 if [ -n "${GSBUCKET}" ]; then
   TIMESTAMP=$(date +'%s')
-  gsutil -m cp "${OUT_ENTRIES}/*" "${GSBUCKET}/${TIMESTAMP}/"
+  "${GSUTIL}" -m cp "${OUT_ENTRIES}/*" "${GSBUCKET}/${TIMESTAMP}/"
   LATEST_FILE="$(mktemp)"
   echo ${TIMESTAMP}>"${LATEST_FILE}"
   "${GSUTIL}" cp "${LATEST_FILE}" "${GSBUCKET}/latest.txt"