Fix incorrect typescript types

[gordonmleigh]

Issue #, if available: #450

Description of changes:

The types are wrong because the javascript exports the functions using module.exports = function and the types declare a named export.

Fixed according to Definitely Typed Best Practices, using export = ....

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.56%. Comparing base (3b89008) to head (afd3bc7).
⚠️ Report is 70 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #699   +/-   ##
=======================================
  Coverage   83.56%   83.56%           
=======================================
  Files          36       36           
  Lines        1813     1813           
=======================================
  Hits         1515     1515           
  Misses        298      298           

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