docs: Fix markdown in TRACING.md

[jodh-intel]

Fix a broken link in TRACING.md.

Fixes #539.

Signed-off-by: James O. D. Hunt james.o.hunt@intel.com

[grahamwhaley]

lgtm

[bergwolf]

/test

[GabyCT]

/test

[teawater]

jenkins-ci-Power8-ubuntu-16-04-initrd fail:

GitHub pull request #540 of commit 3169c9bd969cb58fd9c64424e6789c0110f6b905, no merge conflicts.
Started by user Hui Zhu
Rebuilds build #105
Rebuilds build #106
Rebuilds build #107
Rebuilds build #108
Setting status of 3169c9bd969cb58fd9c64424e6789c0110f6b905 to PENDING with url http://jenkins.katacontainers.io/job/kata-containers-agent-Power8-ubuntu-16-04-PR-initrd/109/ and message: 'Build running'
Using context: jenkins-ci-Power8-ubuntu-16-04-initrd
Building remotely on Power8_slave01 (power8-ubuntu-1604 power8_node) in workspace /home/jenkins/workspace/kata-containers-agent-Power8-ubuntu-16-04-PR-initrd
[WS-CLEANUP] Deleting project workspace...
[WS-CLEANUP] Deferred wipeout is disabled by the job configuration...
ERROR: [WS-CLEANUP] Cannot delete workspace: Unable to delete '/home/jenkins/workspace/kata-containers-agent-Power8-ubuntu-16-04-PR-initrd/go/pkg/linux_ppc64le/github.com/kata-containers/tests/vendor/github.com/BurntSushi/toml.a'. Tried 3 times (of a maximum of 3) waiting 0.1 sec between attempts.
ERROR: Cannot delete workspace: Unable to delete '/home/jenkins/workspace/kata-containers-agent-Power8-ubuntu-16-04-PR-initrd/go/pkg/linux_ppc64le/github.com/kata-containers/tests/vendor/github.com/BurntSushi/toml.a'. Tried 3 times (of a maximum of 3) waiting 0.1 sec between attempts.
Performing Post build task...
Match found for :.* : True
Logical operation result is TRUE
Running script  : #!/bin/bash

export GOPATH=$WORKSPACE/go
export GOROOT="/usr/local/go"
export PATH=${GOPATH}/bin:/usr/local/go/bin:/usr/sbin:/usr/local/bin:${PATH}

cd $GOPATH/src/github.com/kata-containers/tests
.ci/teardown.sh "$WORKSPACE/artifacts"
[kata-containers-agent-Power8-ubuntu-16-04-PR-initrd] $ /bin/bash /tmp/jenkins3468086448414017412.sh
/tmp/jenkins3468086448414017412.sh: line 7: cd: /home/jenkins/workspace/kata-containers-agent-Power8-ubuntu-16-04-PR-initrd/go/src/github.com/kata-containers/tests: No such file or directory
/tmp/jenkins3468086448414017412.sh: line 8: .ci/teardown.sh: No such file or directory
POST BUILD TASK : FAILURE
END OF POST BUILD TASK : 0
Archiving artifacts
Setting status of 3169c9bd969cb58fd9c64424e6789c0110f6b905 to FAILURE with url http://jenkins.katacontainers.io/job/kata-containers-agent-Power8-ubuntu-16-04-PR-initrd/109/ and message: 'Build finished. '
Using context: jenkins-ci-Power8-ubuntu-16-04-initrd
Finished: FAILURE

This PR just change the markdown. So I think this PR does not relate to this fail.