CONTRIBUTING.md: fix markdown link rendering
CONTRIBUTING.md: fix markdown link rendering

Signed-off-by: Ahmet Alp Balkan <c786c8527fd6be7431bb94ca48b6f76cc06787cc@google.com>

GoogleCloudPlatform/kubernetes-engine-samples,GoogleCloudPlatform/kubernetes-engine-samples,GoogleCloudPlatform/kubernetes-engine-samples,mastersingh24/kubernetes-engine-samples,mastersingh24/kubernetes-engine-samples,GoogleCloudPlatform/kubernetes-engine-samples,mastersingh24/kubernetes-engine-samples,GoogleCloudPlatform/kubernetes-engine-samples,mastersingh24/kubernetes-engine-samples,GoogleCloudPlatform/kubernetes-engine-samples,mastersingh24/kubernetes-engine-samples,mastersingh24/kubernetes-engine-samples,mastersingh24/kubernetes-engine-samples,mastersingh24/kubernetes-engine-samples,GoogleCloudPlatform/kubernetes-engine-samples,GoogleCloudPlatform/kubernetes-engine-samples,mastersingh24/kubernetes-engine-samples,GoogleCloudPlatform/kubernetes-engine-samples