verify-generated-docs: Use exit code rather than comparison to empty …

…string

Checking the exit code rather than the empty string has the advantage
that you can identify what was found (comparison consumes the string, so
it's not printed). It makes debugging much easier when something is wrong.

hack/verify-generated-docs.sh

@@ -36,7 +36,7 @@ kube::util::ensure-temp-dir
 kube::util::gen-docs "${KUBE_TEMP}"
 
 # Verify the list matches the expected list (diff should be empty)
-if [[ "$(diff ${KUBE_ROOT}/docs/.generated_docs ${KUBE_TEMP}/docs/.generated_docs)" != "" ]]; then
+if ! diff "${KUBE_ROOT}/docs/.generated_docs" "${KUBE_TEMP}/docs/.generated_docs"; then
   echo "List of generated docs doesn't match a freshly built list. Please run hack/update-generated-docs.sh"
   exit 1
 fi