[SPARK-4421] Wrong link in spark-standalone.html

Modified the link of building Spark.

Author: Masayoshi TSUZUKI <tsudukim@oss.nttdata.co.jp>

Closes #3279 from tsudukim/feature/SPARK-4421 and squashes the following commits:

56e31c1 [Masayoshi TSUZUKI] Modified the link of building Spark.

(cherry picked from commit ddfc09c36381a0880dfa6778be2ca0bc7d80febf)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>