Update README.md

Author: poojanilangekar

extensions/federation/README.md

@@ -7,7 +7,7 @@ NonRESTCatalogs=HADOOP,<alternates>
 
 The other option is to pass it as an argument to the gradle JVM as follows: 
 ```
-./gradlew build DNonRESTCatalogs=HADOOP
+./gradlew build -DNonRESTCatalogs=HADOOP
 ```
 
 Without this flag, the Hadoop factory won't be compiled into Polaris and therefore Polaris will not load the class at runtime, throwing an unsupported exception for federated catalog calls.