fix: Exclude spec files from typedoc generation

[pselden]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Bug fix.

• What is the current behavior? (You can also link to an open issue here)
  Currently spec files are included in typedoc generation, leading to filling your docs with stuff from your tests.

• What is the new behavior (if this is a feature change)?
  Remove spec files from doc generation so they do not show up in your docs.

• Other information:
  See How does exclude work ? TypeStrong/typedoc#170 (comment) for exclude intructions

[codecov]

Codecov Report

Merging #133 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #133   +/-   ##
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  Coverage     100%   100%           
=====================================
  Files           9      9           
  Lines         256    256           
  Branches       38     38           
=====================================
  Hits          256    256

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[bitjson]

@pselden thanks for the PR!