Renaming file and correcting a missing directory (docker#34)

* Rename file

Rename ch02-basic-conceps.adoc to ch02-basic-concepts.adoc

* Corrected path

Added helloworld to path in cd to docker-java-sample

Author: Mano Marks

java/chapters/ch02-basic-conceps.adoc renamed to java/chapters/ch02-basic-concepts.adoc

@@ -218,7 +218,7 @@ Create the Docker image:
 
 [source, text]
 ----
-cd docker-java-sample
+cd docker-java-sample/helloworld
 mvn package -Pdocker
 ----