fix: merge appOptions.data and mount props error

[modai888]

appOptions.data = ()=> ({...appOptions.data, ...props});

When merge appOptions.data and mount props，...appOptions.data is always a function, not an object.

[joeldenning]

This looks reasonable. Ideally we'd add tests for this, but since it took a long time for the maintainers to look at this, I will just merge it as-is.

[joeldenning]

Released in https://github.com/single-spa/single-spa-vue/releases/tag/v3.0.0