[FAB-3340] fix broken link to contributing doc
[FAB-3340] fix broken link to contributing doc

Fix [FAB-3340] by changing link to point to the new location.

[ci-skip]

Change-Id: I35451f7d00e41135b1c659bee107fc448c516457
Signed-off-by: Arnaud J Le Hors <336b2f4fb14e0a6aba0291ba81894e387297584e@us.ibm.com>

ratnakar-asara/fabric-sdk-node,ratnakar-asara/fabric-sdk-node,ratnakar-asara/fabric-sdk-node,ratnakar-asara/fabric-sdk-node,adityachap/fabric-sdk-node,adityachap/fabric-sdk-node