cmServerProtocol: Do not move into json::Value::append()

CMake's copy of json-cpp is not aware of rvalues yet.  It is confusing
to pass the result of std::move to a function that takes a const&
because no move will actually happen.  This change may be reverted once
CMake upgrades to a new version of json-cpp.
60 jobs for lint-fixes
Status Name Job ID Coverage
  External
passed cdash

passed cmake-dash3win7-windows-debug-vs2015

passed cmake-dash3win7-windows-release-ninja

passed cmake-hythloth-linux-debug-makefiles+sphinx

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passed cmake-moonshade-osx-debug-ninja

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00:44:56

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00:19:56

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passed cmake-moonshade-osx-debug-ninja

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passed cmake-moonshade-osx-release-makefiles

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