Corrected a handful of documentation typos.

middleman-core/lib/middleman-core/sitemap/extensions/traversal.rb

@@ -58,7 +58,7 @@ module Middleman
           parent.children.reject { |p| p == self }
         end
 
-        # Whether this resource either a directory index, or has the same name as an existing directory in the source
+        # Whether this resource is either a directory index, or has the same name as an existing directory in the source
         # @return [Boolean]
         def directory_index?
           path.include?(app.config[:index_file]) || path =~ /\/$/ || eponymous_directory?

middleman-core/lib/middleman-core/sitemap/resource.rb

@@ -73,7 +73,7 @@ module Middleman
       end
 
       # Merge in new metadata specific to this resource.
-      # @param [Hash] metadata A metadata block like provides_metadata_for_path takes
+      # @param [Hash] meta A metadata block like provides_metadata_for_path takes
       def add_metadata(meta={})
         @local_metadata.deep_merge!(meta.dup)
       end

middleman-core/lib/middleman-core/util.rb

@@ -113,7 +113,7 @@ module Middleman
         end
       end
 
-      # Get a recusive list of files inside a set of paths.
+      # Get a recursive list of files inside a set of paths.
       # Works with symlinks.
       #
       # @param paths Some paths string or Pathname