test(WDIO): Don't run tests if the build folder doesn't exist close #167
test(WDIO): Don't run tests if the build folder doesn't exist close #167

Don't run visual regression tests if the build folder doesn't exists.
This avoids burying the instruction to run `npm run docs` in other error reports.

stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila