workspace-status.sh: quote 'tr' arguments.

Otherwise, the shell may interpret [a-z], leading to version strings
such as

  STABLE_BUILD_superm[nifest_LABEL 6010213-dirty

Change-Id: I5846efc03419e7361d3171df14646c96f66118ac

tools/workspace-status.sh

@@ -17,6 +17,6 @@ function rev() {
 echo STABLE_BUILD_GERRIT_LABEL $(rev .)
 for p in plugins/* ; do
   test -d "$p" || continue
-  echo STABLE_BUILD_$(echo $(basename $p)_LABEL|tr [a-z] [A-Z]) $(rev $p)
+  echo STABLE_BUILD_$(echo $(basename $p)_LABEL|tr '[a-z]' '[A-Z]' ) $(rev $p)
 done
 echo "STABLE_WORKSPACE_ROOT ${PWD}"