Resolve reduce of empty array with no initial val

In case that there are no projects in jira it will start displaying error bellow due to array being empty and no initial value for reduce.

[Mon Oct 05 2015 03:03:21 GMT-0400 (EDT)] ERROR TypeError: Reduce of empty array with no initial value
  at Array.reduce (native)
  at /usr/local/xxx/node_modules/hubot-scripts/src/scripts/jira-issues.coffee:42:7, <js>:27:38
  at IncomingMessage.<anonymous> (/usr/local/bender/node_modules/hubot/node_modules/scoped-http-client/src/index.js:95:22)
  at IncomingMessage.emit (events.js:117:20)
  at _stream_readable.js:944:16
  at process._tickCallback (node.js:448:13)

src/scripts/jira-issues.coffee

@@ -39,7 +39,7 @@ module.exports = (robot) ->
     .get() (err, res, body) ->
       json = JSON.parse(body)
       jiraPrefixes = ( entry.key for entry in json )
-      reducedPrefixes = jiraPrefixes.reduce (x,y) -> x + "-|" + y
+      reducedPrefixes = jiraPrefixes.reduce ((x,y) -> x + "-|" + y), 0
       jiraPattern = "/\\b(" + reducedPrefixes + "-)(\\d+)\\b/g"
       ic = process.env.HUBOT_JIRA_IGNORECASE
       if ic == undefined || ic == "true"