[cron] fix yet another bug diana found :)

Change-Id: I0566bb95c43c6b6b09553102287cfe4f417dfa66
diff --git a/helpers/llvm-cron-build b/helpers/llvm-cron-build
index a0af680..9d2062b 100755
--- a/helpers/llvm-cron-build
+++ b/helpers/llvm-cron-build
@@ -45,7 +45,7 @@
 fi
 
 # Crontab-specific, make sure the helpers directory is in the path
-if [ $(echo "$PATH" | grep "$ROOT") == "" ]; then
+if [ "$(echo "$PATH" | grep "$ROOT")" = "" ]; then
   PATH="$PATH":"$ROOT"
 fi