analytics.sh: use full uuidgen path on OS X.

Fixes #575.

Library/Homebrew/utils/analytics.sh

@@ -38,6 +38,9 @@ setup-analytics() {
     if [[ -n "$HOMEBREW_LINUX" ]]
     then
       HOMEBREW_ANALYTICS_USER_UUID="$(tr a-f A-F < /proc/sys/kernel/random/uuid)"
+    elif [[ -n "$HOMEBREW_OSX" ]]
+    then
+      HOMEBREW_ANALYTICS_USER_UUID="$(/usr/bin/uuidgen)"
     else
       HOMEBREW_ANALYTICS_USER_UUID="$(uuidgen)"
     fi