use BSON::ObjectId rather than Mongo::ObjectId for return values in doc

lib/bson/types/object_id.rb

@@ -68,7 +68,7 @@ module BSON
     #   succeeding the timestamp will be zeroed; if true, they'll
     #   consist of the standard machine id, pid, and counter.
     #
-    # @return [Mongo::ObjectId]
+    # @return [BSON::ObjectId]
     #
     # @example Return all document created before Jan 1, 2010.
     #   time = Time.utc(2010, 1, 1)
@@ -87,7 +87,7 @@ module BSON
     #
     # @param [Hash] doc a document requiring an _id.
     #
-    # @return [Mongo::ObjectId, Object] returns a newly-created or 
+    # @return [BSON::ObjectId, Object] returns a newly-created or 
     #   current _id for the given document.
     def self.create_pk(doc)
       doc.has_key?(:_id) || doc.has_key?('_id') ? doc : doc.merge!(:_id => self.new)
@@ -121,7 +121,7 @@ module BSON
     #
     # @param [String] str
     #
-    # @return [Mongo::ObjectId]
+    # @return [BSON::ObjectId]
     def self.from_string(str)
       raise InvalidObjectId, "illegal ObjectId format: #{str}" unless legal?(str)
       data = []

lib/mongo/db.rb

@@ -63,7 +63,7 @@ module Mongo
     # @option opts [Boolean] :strict (False) If true, collections must exist to be accessed and must
     #   not exist to be created. See DB#collection and DB#create_collection.
     #
-    # @option opts [Object, #create_pk(doc)] :pk (Mongo::ObjectId) A primary key factory object,
+    # @option opts [Object, #create_pk(doc)] :pk (BSON::ObjectId) A primary key factory object,
     #   which should take a hash and return a hash which merges the original hash with any primary key
     #   fields the factory wishes to inject. (NOTE: if the object already has a primary key,
     #   the factory should not inject a new key).

lib/mongo/gridfs/grid.rb

@@ -63,7 +63,7 @@ module Mongo
     # @option opts [Boolean] :safe (false) When safe mode is enabled, the chunks sent to the server
     #   will be validated using an md5 hash. If validation fails, an exception will be raised.
     #
-    # @return [Mongo::ObjectId] the file's id.
+    # @return [BSON::ObjectId] the file's id.
     def put(data, opts={})
       opts     = opts.dup
       filename = opts[:filename]