maven-download-plugin CachedFileEntry issue. Fix or add description to ReadMe

[vdiravka]

Issue:
mvn clean install -DskipTests

[INFO] Google DoubleClick Libraries ....................... SUCCESS [  0.577 s]
[INFO] Google DoubleClick Core ............................ SUCCESS [ 13.613 s]
[INFO] Google DoubleClick OpenRTB ......................... FAILURE [  0.806 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  15.142 s
[INFO] Finished at: 2020-04-17T15:07:28+03:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.googlecode.maven-download-plugin:download-maven-plugin:1.4.2:wget (include-openrtb-proto) on project doubleclick-openrtb: Execution include-openrtb-proto of goal com.googlecode.maven-download-plugin:download-maven-plugin:1.4.2:wget failed: java.lang.ClassNotFoundException: com.googlecode.download.maven.plugin.internal.CachedFileEntry -> [Help 1]

Solution:
$ sudo rm -r ~/.m2/repository/.cache/download-maven-plugin/

[opinali]

This is an interesting problem, is there a particular scenario that makes this error happen (i.e. do you have a repro)? It would be ideal to add that to the readme if possible.