[doc] contributing: fixed unordered list formatting
[doc] contributing: fixed unordered list formatting

Change-Id: I0d96e28767331ae81ff90f42dd5e68a5b3b83ab8
Reviewed-on: http://gerrit.cloudera.org:8080/5066
Reviewed-by: Will Berkeley <c74686ab413a71926fc1bc9d16ebfa30e619336a@gmail.com>
Tested-by: Kudu Jenkins

andrwng/kudu,cloudera/kudu,helifu/kudu,cloudera/kudu,helifu/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,cloudera/kudu,andrwng/kudu,helifu/kudu,andrwng/kudu,InspurUSA/kudu,cloudera/kudu,andrwng/kudu,cloudera/kudu,cloudera/kudu,InspurUSA/kudu,andrwng/kudu,InspurUSA/kudu,andrwng/kudu,andrwng/kudu,InspurUSA/kudu,cloudera/kudu,helifu/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,andrwng/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,cloudera/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,helifu/kudu,cloudera/kudu,InspurUSA/kudu,helifu/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,andrwng/kudu,helifu/kudu