buildbot failure in on flink-docs-release-1.0

[buildbot]

The Buildbot has detected a new failure on builder flink-docs-release-1.0 while 
building . Full details are available at:
    https://ci.apache.org/builders/flink-docs-release-1.0/builds/37

Buildbot URL: https://ci.apache.org/

Buildslave for this Build: lares_ubuntu

Build Reason: forced: by IRC user <uce> on channel #flink-testing: build me the 
docs please
Build Source Stamp: HEAD
Blamelist: 

BUILD FAILED: failed compile

Sincerely,
 -The Buildbot