Retry downloading dynamodb if it fails.

.travis.yml

@@ -55,7 +55,7 @@ before_install:
           if [[ "$TOXENV" == *dynamodb ]]; then
               sudo apt-get install -y default-jre supervisor
               mkdir /opt/dynamodb-local
-              cd /opt/dynamodb-local && curl -L http://dynamodb-local.s3-website-us-west-2.amazonaws.com/dynamodb_local_latest.tar.gz | tar zx
+              cd /opt/dynamodb-local && curl --retry 5 --retry-delay 1 -L http://dynamodb-local.s3-website-us-west-2.amazonaws.com/dynamodb_local_latest.tar.gz | tar zx
               cd -
               echo '[program:dynamodb-local]' | sudo tee /etc/supervisor/conf.d/dynamodb-local.conf
               echo 'command=java -Djava.library.path=./DynamoDBLocal_lib -jar DynamoDBLocal.jar -inMemory' | sudo tee -a /etc/supervisor/conf.d/dynamodb-local.conf