Fix "Client vendor file sourcemap gets compiled" tests

[KevinGrandon]

After 959f73e landed there are perma-failures in master CI.

Example failure:

not ok 111 Client vendor file gets compiled
  ---
    operator: ok
    expected: true
    actual:   false
    at: Test.test (/fusion-cli/test/cli/build.js:91:5)
  ...
not ok 112 Client vendor file sourcemap gets compiled
  ---
    operator: ok
    expected: true
    actual:   false
at: Test.test (/fusion-cli/test/cli/build.js:92:5)