fix: hard corded region and stack name of api_cognito_auth example

[53ningen]

Issue #, if available:
none

Description of changes:

• region and stack-name of api_cognito_auth example was hard corded.
  • when I create stack on us-west-2 region, npm run open-login-page command returns wrong login-page.
  • when I create stack named hoge, npm run configure-cognito-user-pool command fails.
• I fixed hard corded region and stack-name parameters in package.json

Description of how you validated changes:

After I run the commands below, I verified the example worked well.

• npm run package-deploy
• npm run configure-cognito-user-pool

Checklist:

• [-] Write/update tests
• [-] make pr passes
• [-] Update documentation
• [-] Verify transformed template deploys and application functions as expected
• [-] Add/update example to examples/2016-10-31

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

[codecov-io]

Codecov Report

Merging #1049 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #1049   +/-   ##
========================================
  Coverage    94.77%   94.77%           
========================================
  Files           69       69           
  Lines         3256     3256           
  Branches       635      635           
========================================
  Hits          3086     3086           
  Misses          88       88           
  Partials        82       82

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[jlhood]

@53ningen Thanks so much for fixing this!