[#1589] Remove invalid URL from README.md

fixes #1589

Author: dobraczka

README.md

@@ -6,7 +6,7 @@
 
 ## Gradoop: Distributed Graph Analytics on Hadoop
 
-[Gradoop](http://www.gradoop.com) is an open source (ALv2) research framework for scalable 
+Gradoop is an open source (ALv2) research framework for scalable 
 graph analytics built on top of [Apache Flink](http://flink.apache.org/). It offers a graph data model which 
 extends the widespread [property graph model](https://github.com/tinkerpop/blueprints/wiki/Property-Graph-Model) 
 by the concept of logical graphs and further provides operators that can be applied