Enable customized dynamoDB client, fix typos and bump version to 1.0.25

This release added a dynamoDBClient property in alexaRequestHandler so that developer can use their own dynamoDB client, if the dynamDBClient is null, then it will use the default one. The example code of inserting dynamoDB client is as blow:

exports.handler = function(event, context, callback) {
    const alexa = Alexa.handler(event, context);
    alexa.dynamoDBClient = new aws.DynamoDB({
         endpoint: "http://localhost:8000",
         apiVersion: '2012-08-10'
     });
     ...
}