Fix some yarddoc issues

lib/rex/mime/part.rb

@@ -36,8 +36,8 @@ class Part
 
   # Returns the Content-Transfer-Encoding of the part.
   #
-  # @returns [nil] if the part hasn't Content-Transfer-Encoding.
-  # @returns [String] The Content-Transfer-Encoding or the part.
+  # @return [nil] if the part hasn't Content-Transfer-Encoding.
+  # @return [String] The Content-Transfer-Encoding or the part.
   def transfer_encoding
     h = header.find('Content-Transfer-Encoding')
     return nil if h.nil?

lib/rex/post/meterpreter/extensions/extapi/adsi/adsi.rb

@@ -32,7 +32,7 @@ class Adsi
   # @param fields [Array] Array of string fields to return for
   #   each result found
   #
-  # @returns [Hash] Array of field names with associated results.
+  # @return [Hash] Array of field names with associated results.
   #
   def domain_query(domain_name, filter, max_results, page_size, fields)
     request = Packet.create_request('extapi_adsi_domain_query')

lib/rex/post/meterpreter/extensions/extapi/wmi/wmi.rb

@@ -26,7 +26,7 @@ class Wmi
   # @param root [String] Specify root to target, otherwise defaults
   #   to 'root\cimv2'
   #
-  # @returns [Hash] Array of field names with associated values.
+  # @return [Hash] Array of field names with associated values.
   #
   def query(query, root = nil)
     request = Packet.create_request('extapi_wmi_query')