Recognise ^6, >=5 etc as valid semver

[JamieMason]

Description

✘ npm has mismatched versions which syncpack cannot fix
  ^6 in engines.npm of package.json
  >=5 in engines.npm of packages/framework/fluid-framework/package.json
  ^5 in engines.npm of packages/framework/tinylicious-client/package.json

As a workaround, adding .0.0 to the end of those versions will cause syncpack to recognise them as semver.

Suggested Solution

1. Add examples of these kinds of versions to /src/lib/is-semver.spec.ts
2. Edit isSemver(version: unknown): boolean so the tests pass.

[JamieMason]

Released in 9.7.4