followed this

https://github.com/apache/spark/blob/master/docs/README.md

to build spark docs,but it hangs on:

SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.

after half an hour,no further info got printed out.I tried to add slf4j-simple-1.7.12.jar into spark/lib_managed/jars,then rerun

jekyll build

still hang on these messages,how to solve the problem?