Current vue support requires undeclared peer dep on `vue`

[dlongley]

If @bedrock/karma is used in a non-vue project (vue is not installed anywhere), the test running fails with the error:

Error: Cannot find module 'vue/compiler-sfc'

Installing vue in the test directory alongside @bedrock/karma fixes the error, but seems like the wrong solution. Either @bedrock/karma should install vue as a dependency or list it as a peer dependency -- or, even better, there should be some way to run non-vue module tests without installing vue at all.