Update Rake task for generating docs to different dir and fix documentation

Author: estolfo

Rakefile

@@ -36,7 +36,7 @@ task :docs => 'docs:yard'
 namespace :docs do
   desc "Generate yard documention"
   task :yard do
-    out = File.join('docs', Mongo::VERSION)
+    out = File.join('yard-docs', Mongo::VERSION)
     FileUtils.rm_rf(out)
     system "yardoc -o #{out} --title mongo-#{Mongo::VERSION}"
   end

lib/mongo/grid/file/chunk.rb

@@ -162,8 +162,9 @@ def assemble(chunks)
           # @example Split the data into chunks.
           #   Chunks.split(data)
           #
-          # @param [ String, IO ] data The raw bytes.
+          # @param [ String, IO ] io The raw bytes.
           # @param [ File::Info ] file_info The files collection file doc.
+          # @param [ Integer ] offset The offset.
           #
           # @return [ Array<Chunk> ] The chunks of the data.
           #