Fix typo in error message printed if ran under virtualenv

Commit title says it all. I don't know how you feel about these kind
of commits, I feel like it's a waste of resources but I also feel bad
when I see big/obvious typo.

Change-Id: If048bb2dbad1a0b5a13e56b5fa1e6ea7c01eb05e
diff --git a/stack.sh b/stack.sh
index 825ed96..36bf2af 100755
--- a/stack.sh
+++ b/stack.sh
@@ -99,10 +99,10 @@
 # this explicit as it has come up on the mailing list.
 if [[ -n "$VIRTUAL_ENV" ]]; then
     echo "You appear to be running under a python virtualenv."
-    echo "DevStack does not support this, as we my break the"
+    echo "DevStack does not support this, as we may break the"
     echo "virtualenv you are currently in by modifying "
     echo "external system-level components the virtualenv relies on."
-    echo "We reccommend you use a separate virtual-machine if "
+    echo "We recommend you use a separate virtual-machine if "
     echo "you are worried about DevStack taking over your system."
     exit 1
 fi