fix: use typescript import/export for gapics

[callmehiphop]

Fixes #610

• Tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

[codecov]

Codecov Report

Merging #611 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #611      +/-   ##
==========================================
+ Coverage   97.89%   97.89%   +<.01%     
==========================================
  Files          14       14              
  Lines         856      857       +1     
  Branches      178      178              
==========================================
+ Hits          838      839       +1     
  Misses          2        2              
  Partials       16       16

Impacted Files	Coverage Δ
src/index.ts	100% <100%> (ø)	⬆️

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