Fix import via SPM

[larryonoff]

This's strange but I'm trying to replicate the error that I and, but not able yet :)

[larryonoff]

@johnxnguyen could you please check this PR and if it's fine make new release?

[johnxnguyen]

@larryonoff my apologies for the delayed responses, I've been a bit of sick leave recently and back to a busy work schedule so time has been scarce.

I'm not sure I fully understand the problem this PR is solving, could you give some more context please?

Also, travis has been acting up lately and not running tests so I need to fix that first. I'm considering switching to another CI provider.

[larryonoff]

@johnxnguyen our team develops internal framework. Some of the packages use external dependencies like Down. The structure of our main app is: App imports InternalSDK.PackageX, InternalSDK.PackageX imports Down.

We started migration to SPM from Cococapods recently. But we had an error with Down: Missing required module 'libcmark'. No such module 'libcmark'.

This PR should fix it.

PS. Strange thing that I cannot reproduce the issue now using the tag 0.11.

[larryonoff]

Cleaned the project, updated all dependencies. As result "Missing required module 'libcmark'" for the current tag 0.11

[codecov]

Codecov Report

Merging #268 (9dd46e0) into master (3b07bb5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #268   +/-   ##
=======================================
  Coverage   91.15%   91.15%           
=======================================
  Files          60       60           
  Lines        1063     1063           
=======================================
  Hits          969      969           
  Misses         94       94           

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