Don't set default avatar url on ENV

Fingerprinting filter that Brocolli uses to add checksums to filenames
apparently is very greedy. When a URL that has a valid image is present
in ENV, fingerprint filter will going to wipe out the entire config's
meta tag value with fingerprinted url with an asset host.

app/utils/urls.coffee

@@ -39,6 +39,7 @@ email = (email) ->
   "mailto:#{email}"
 
 gravatarImage = (email, size) ->
-  "https://www.gravatar.com/avatar/#{md5(email)}?s=#{size}&d=#{encodeURIComponent(config.avatarDefaultUrl)}"
+  avatarDefaultUrl = 'https://travis-ci.org/images/ui/default-avatar.png'
+  "https://www.gravatar.com/avatar/#{md5(email)}?s=#{size}&d=#{encodeURIComponent(avatarDefaultUrl)}"
 
 `export { plainTextLog, githubPullRequest, githubCommit, githubRepo, githubWatchers, githubNetwork, githubAdmin, statusImage, ccXml, email, gravatarImage }`

config/environment.js

@@ -28,8 +28,7 @@ module.exports = function(environment) {
     pro: false,
     enterprise: false,
     endpoints: {},
-    intervals: { updateTimes: 1000 },
-    avatarDefaultUrl: 'https://travis-ci.org/images/ui/default-avatar.png'
+    intervals: { updateTimes: 1000 }
   };
 
   if (typeof process !== 'undefined') {