Update README.md

Author: derjust

README.md

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 # Spring  Data DynamoDB #
 
-<img align="left" src="banner/spring-data-dynamodb.png" />
+<img align="left" src="https://spring-data-dynamodb.github.io/spring-data-dynamodb/banner/spring-data-dynamodb.png" />
 
 The primary goal of the [Spring® Data](http://www.springsource.org/spring-data) project is to make it easier to build Spring-powered applications that use data access technologies.