update-bazel.sh: fix on Mac

hack/update-bazel.sh

@@ -20,6 +20,15 @@ set -o pipefail
 export KUBE_ROOT=$(dirname "${BASH_SOURCE}")/..
 source "${KUBE_ROOT}/hack/lib/init.sh"
 
+if LANG=C sed --help 2>&1 | grep -q GNU; then
+  SED="sed"
+elif which gsed &>/dev/null; then
+  SED="gsed"
+else
+  echo "Failed to find GNU sed as sed or gsed. If you are on Mac: brew install gnu-sed." >&2
+  exit 1
+fi
+
 # Remove generated files prior to running kazel.
 # TODO(spxtr): Remove this line once Bazel is the only way to build.
 rm -f "${KUBE_ROOT}/pkg/generated/openapi/zz_generated.openapi.go"
@@ -44,6 +53,6 @@ gazelle fix \
 # gazelle won't follow the symlinks in vendor/, so we can't just exclude
 # staging/. Instead we just fix the bad paths with sed.
 find staging -name BUILD -o -name BUILD.bazel | \
-  xargs sed -i 's|\(importpath = "\)k8s.io/kubernetes/staging/src/\(.*\)|\1\2|'
+  xargs ${SED} -i 's|\(importpath = "\)k8s.io/kubernetes/staging/src/\(.*\)|\1\2|'
 
 kazel