Remove volatile() property modifier

The modifier got deprecated and wasn't actually needed in any of the used cases.

app/controllers/dashboard/contributions/show.js

@@ -7,6 +7,6 @@ export default Controller.extend({
 
   ipfsGatewayUrl: computed(function() {
     return config.ipfs.gatewayUrl;
-  }).volatile()
+  })
 
 });

app/controllers/dashboard/contributors/show.js

@@ -12,6 +12,6 @@ export default Controller.extend({
 
   ipfsGatewayUrl: computed(function() {
     return config.ipfs.gatewayUrl;
-  }).volatile()
+  })
 
 });