Use Regexp#=== to match loosely

Till ruby 2.5, `Object#=~` silently ignored non-string argument,
but it has been deprecated since ruby 2.6 and will be removed in
the future.  Use `Regexp#===` instead, to match loosely.

Also `/^-/` is not a proper pattern to tell if the argument starts
with a `-`.

lib/rake/application.rb

@@ -392,7 +392,7 @@ def trace(*strings) # :nodoc:
 
     def sort_options(options) # :nodoc:
       options.sort_by { |opt|
-        opt.select { |o| o =~ /^-/ }.map(&:downcase).sort.reverse
+        opt.select { |o| /\A-/ === o }.map(&:downcase).sort.reverse
       }
     end
     private :sort_options