CI: Use markdown link syntax in gitter messages

Author: cameel

.circleci/config.yml

@@ -43,8 +43,8 @@ commands:
       - run:
           name: "Gitter notification"
           command: |
-            [[ "<< parameters.event >>" == "failure" ]] && message=" ❌ Nightly job **${CIRCLE_JOB}** failed on **${CIRCLE_BRANCH}**. Please see ${CIRCLE_BUILD_URL} for details."
-            [[ "<< parameters.event >>" == "success" ]] && message=" ✅ Nightly job **${CIRCLE_JOB}** succeeded on **${CIRCLE_BRANCH}**. Please see ${CIRCLE_BUILD_URL} for details."
+            [[ "<< parameters.event >>" == "failure" ]] && message=" ❌ Nightly job **${CIRCLE_JOB}** failed on **${CIRCLE_BRANCH}**. Please see [build #${CIRCLE_BUILD_NUM}](${CIRCLE_BUILD_URL}) for details."
+            [[ "<< parameters.event >>" == "success" ]] && message=" ✅ Nightly job **${CIRCLE_JOB}** succeeded on **${CIRCLE_BRANCH}**. Please see [build #${CIRCLE_BUILD_NUM}](${CIRCLE_BUILD_URL}) for details."
 
             curl "https://api.gitter.im/v1/rooms/${GITTER_NOTIFY_ROOM_ID}/chatMessages" \
               --request POST \