Fix Performance/UnfreezeString Rubocop offences.

Author: hainesr

.rubocop_todo.yml

@@ -21,13 +21,6 @@ Layout/LineContinuationSpacing:
   Exclude:
     - 'lib/zip/bzip2/errors.rb'
 
-# Offense count: 3
-# This cop supports unsafe autocorrection (--autocorrect-all).
-Performance/UnfreezeString:
-  Exclude:
-    - 'lib/zip/bzip2/decompress.rb'
-    - 'lib/zip/bzip2/decompressor.rb'
-
 # Offense count: 9
 # This cop supports safe autocorrection (--autocorrect).
 Style/FileRead:

lib/zip/bzip2/decompress.rb

@@ -18,7 +18,7 @@ def initialize(options = {})
       end
 
       def decompress(data)
-        result = ''.dup
+        result = +''
 
         with_input_buffer(data) do |input_buffer|
           @libbz2.input_buffer = input_buffer

lib/zip/bzip2/decompressor.rb

@@ -8,11 +8,11 @@ class Decompressor < ::Zip::Decompressor #:nodoc:
       def initialize(*args)
         super
 
-        @buffer = ''.dup
+        @buffer = +''
         @bzip2_ffi_decompressor = ::Zip::Bzip2::Decompress.new
       end
 
-      def read(length = nil, outbuf = ''.dup)
+      def read(length = nil, outbuf = +'')
         return return_value_on_eof(length) if eof
 
         fill_buffer(length)