Fix comment wording nit

Change-Id: I558522121099f14d380c163a2c397b34335b03df
diff --git a/stack.sh b/stack.sh
index 10ffc5e..08cdbe4 100755
--- a/stack.sh
+++ b/stack.sh
@@ -537,7 +537,7 @@
 
     if [[ $r -ne 0 ]]; then
         echo "Error on exit"
-        # If we error before we've installed os-testr, which will fail.
+        # If we error before we've installed os-testr, this will fail.
         if type -p generate-subunit > /dev/null; then
             generate-subunit $DEVSTACK_START_TIME $SECONDS 'fail' >> ${SUBUNIT_OUTPUT}
         fi
@@ -547,7 +547,7 @@
             $TOP_DIR/tools/worlddump.py -d $LOGDIR
         fi
     else
-        # If we error before we've installed os-testr, which will fail.
+        # If we error before we've installed os-testr, this will fail.
         if type -p generate-subunit > /dev/null; then
             generate-subunit $DEVSTACK_START_TIME $SECONDS >> ${SUBUNIT_OUTPUT}
         fi