fixed correlation_matrix_test.cpp

#### Summary:

Fixes the correlation_matrix test. Only touches the single test, no code.

#### Intended Effect:

Fixes the test.

#### How to Verify:

Run: `make test/CmdStan/models/transforms/correlation_matrix`. 

Before the fix, this individual test would fail from a clean build. This was masked when running all tests because the model that was called from the test was built with the bounded_model test.

#### Side Effects:

No.

#### Documentation:

Not user facing.

#### Reviewer Suggestions:

Anyone.