make sure we use a valid US area code

[dczulada]

Pull requests into Cypress require the following. Submitter and reviewer should :white_check_mark: when done. For items that are not-applicable, note it's not-applicable ("N/A") and :white_check_mark:.

Submitter:

• [ ] This pull request describes why these changes were made.
• [ ] Internal ticket for this PR:
• [ ] Internal ticket links to this PR
• [ ] Code diff has been done and been reviewed
• [ ] Tests are included and test edge cases
• [ ] Tests have been run locally and pass

Reviewer 1:

Name:

• [ ] Code is maintainable and reusable, reuses existing code and infrastructure where appropriate, and accomplishes the task’s purpose
• [ ] The tests appropriately test the new code, including edge cases
• [ ] You have tried to break the code

Reviewer 2:

Name:

• [ ] Code is maintainable and reusable, reuses existing code and infrastructure where appropriate, and accomplishes the task’s purpose
• [ ] The tests appropriately test the new code, including edge cases
• [ ] You have tried to break the code

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (07f8430) 96.74% compared to head (77b58b8) 96.74%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1813 +/- ## ======================================= Coverage 96.74% 96.74% ======================================= Files 156 156 Lines 7040 7044 +4 ======================================= + Hits 6811 6815 +4 Misses 229 229 ``` | [Impacted Files](https://app.codecov.io/gh/projectcypress/cypress/pull/1813?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=projectcypress) | Coverage Δ | | |---|---|---| | [lib/cypress/demographics\_randomizer.rb](https://app.codecov.io/gh/projectcypress/cypress/pull/1813?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=projectcypress#diff-bGliL2N5cHJlc3MvZGVtb2dyYXBoaWNzX3JhbmRvbWl6ZXIucmI=) | `100.00% <100.00%> (ø)` | |

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