Don't try to Time.parse a "Time" object

With Ruby2.7, Time can't be converted into a String implicitly. The way
we use Time.parse, we don't need to convert the Time object into a
String just to convert it into a Time object again (using Time.parse).

Fixes #815.

app/controllers/application_controller.rb

@@ -82,7 +82,7 @@ def set_releases_parameters
       now = Time.now
       versions.each do |version|
         version['releases'].reject! do |release|
-          release['date'] = Time.parse(release['date'])
+          release['date'] = Time.parse(release['date']) unless release['date']
           release['date'] > now
         end
         # Get the latest release