Set Cache-Control header on badges

Since github caches external resource we need to indicate that this
badge is supposed to be changing.

https://github.com/github/markup/issues/224

Handler/Package.hs

@@ -27,6 +27,7 @@ getPackageR = packagePage Nothing
 
 getPackageBadgeR :: PackageName -> SnapshotBranch -> Handler TypedContent
 getPackageBadgeR pname branch = do
+    cacheSeconds (3 * 60 * 60)
     snapName     <- maybe notFound pure =<< newestSnapshot branch
     Entity sid _ <- maybe notFound pure =<< lookupSnapshot snapName
     mVersion <- do mSnapPackage <- lookupSnapshotPackage sid (unPackageName pname)