doc error fix

[niejunhao]

What kind of change does this PR introduce? (check one with "x")

[] Bugfix
[] Feature
[] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[] Other... Please describe:

Fixes: # docs

What is the current behavior?

What is the new behavior?

[flogo-oss]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[lixingwang]

Thanks for your PR. Looks good to me.

[mellistibco]

looks good! please accept the cla and we''ll merge into master.

[lixingwang]

@niejunhao Could you please accept CLA and we can merge this into master?