Fixed the doc examples for Indexes to use the new Meta syntax.
Fixed the doc examples for Indexes to use the new Meta syntax.

Villoid/PynamoDB,mtsgrd/PynamoDB2,khwilson/PynamoDB,pynamodb/PynamoDB,mpresh/PynamoDB,borgstrom/PynamoDB,jlafon/PynamoDB,mpresh/PynamoDB,Evzdrop/PynamoDB,joshowen/PynamoDB