fix(Filesystem utilities): Use `path().is_dir()` so that symlinks are resolved
fix(Filesystem utilities): Use `path().is_dir()` so that symlinks are resolved

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