Update service_controller.rst

The word "it's" is a contraction for "it is".  "Its" is a possessive pronoun.
minor #956 Update service_controller.rst (cxj)

This PR was submitted for the master branch but it was merged into the 1.2 branch instead (closes #956).

Discussion
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Update service_controller.rst

The word "it's" is a contraction for "it is".  "Its" is a possessive pronoun.

Commits
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09a5fe3 Update service_controller.rst