style: use RuboCop 0.41.1 (#433)

Tweak `Style/NumericLiteralPrefix` cop settings as we're using octal
literals a lot (both in formulae and the package manager) for file
permissions and aren't ready just yet to transition them to the more
beginner-friendly `0o` prefix (instead of the more obscure `0` prefix).

Library/.rubocop.yml

@@ -66,6 +66,10 @@ Style/EmptyLineBetweenDefs:
 Style/NumericLiterals:
   Enabled: false
 
+# zero-prefixed octal literals are just too widely used (and mostly understood)
+Style/NumericLiteralPrefix:
+  EnforcedOctalStyle: zero_only
+
 # consistency and readability when faced with string interpolation
 Style/PercentLiteralDelimiters:
   PreferredDelimiters:

Library/Homebrew/cmd/style.rb

@@ -47,7 +47,7 @@ module Homebrew
 
   def check_style_impl(files, output_type, options = {})
     fix = options[:fix]
-    Homebrew.install_gem_setup_path! "rubocop", "0.40"
+    Homebrew.install_gem_setup_path! "rubocop", "0.41.1"
 
     args = %W[
       --force-exclusion