moved expresso to devDependencies

Author: lackac

package.json

@@ -6,7 +6,7 @@
   "repository": "git://github.com/elbart/node-memcache.git",
   "author": "Tim Eggert <tim@elbart.com>",
   "main": "./lib/memcache",
-  "dependencies": {
+  "devDependencies": {
     "expresso": ">=0.7.0"
   },
   "directories": {