Fixed typo which was referring to 'imports' section and not 'setup'

[matthewhegarty]

I noticed that there is a v minor typo in the testing guide. The second code block for app/banner.component.spec.ts duplicates the '(imports)' text

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[matthewhegarty]

I signed it!

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[wardbell]

Good catch! I have a large number of changes stacked up in pr #2396 so I've incorporated this one in that PR.