rubocop: disable Performance/RedundantBlockCall

It suggests changes like this:

    diff --git a/lib/tasks/book2.rake b/lib/tasks/book2.rake
    index 046f35f3..f083f25a 100644
    --- a/lib/tasks/book2.rake
    +++ b/lib/tasks/book2.rake
    @@ -11,9 +11,9 @@ def expand(content, path, &get_content)
         else
           new_fname = (Pathname.new(path).dirname + Pathname.new($1)).cleanpath.to_s
         end
    -    new_content = get_content.call(new_fname)
    +    new_content = yield(new_fname)
         if new_content
    -      expand(new_content.gsub("\xEF\xBB\xBF".force_encoding("UTF-8"), ""), new_fname) { |c| get_content.call (c) }
    +      expand(new_content.gsub("\xEF\xBB\xBF".force_encoding("UTF-8"), ""), new_fname) { |c| yield (c) }
         else
           puts "#{new_fname} could not be resolved for expansion"
           ""

That's not wrong, but it seems weird to me to yield in a function that
takes a bunch of parameters. Yes, the get_content function passed in
_happens_ to be the final one, but it doesn't have to be.

.rubocop.yml

@@ -10,6 +10,8 @@ AllCops:
 
 Performance:
   enabled: true
+Performance/RedundantBlockCall:
+  Enabled: false
 
 Style:
   Exclude: