Added sandbox to the Environment Enum.

[samuelpx]

Reason for PR:

While testing using a sandbox application, the following error was observed:

Exception in thread "main" com.squareup.moshi.JsonDataException: Expected one of [production, staging] but was sandbox at path $.data.environment
at com.squareup.moshi.StandardJsonAdapters$EnumJsonAdapter.fromJson(StandardJsonAdapters.java:296)
at com.squareup.moshi.StandardJsonAdapters$EnumJsonAdapter.fromJson(StandardJsonAdapters.java:264)
at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
at com.squareup.moshi.kotlin.reflect.KotlinJsonAdapter.fromJson(KotlinJsonAdapter.kt:86)
at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
at com.squareup.moshi.kotlin.reflect.KotlinJsonAdapter.fromJson(KotlinJsonAdapter.kt:86)
at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
at com.squareup.moshi.JsonAdapter.fromJson(JsonAdapter.java:58)
at com.nylas.NylasClient.executeRequest(NylasClient.kt:357)
at com.nylas.NylasClient.executeGet(NylasClient.kt:202)
at com.nylas.NylasClient.executeGet$default(NylasClient.kt:195)
at com.nylas.resources.Applications.getDetails(Applications.kt:31)
at com.nylas.resources.Applications.getDetails$default(Applications.kt:28)
at com.nylas.resources.Applications.getDetails(Applications.kt)
at com.example.NylasTest.main(NylasTest.java:8)

This PR should correct the error and make testing easier for new users

License

I confirm that this contribution is made under the terms of the MIT license and that I have the authority necessary to make this contribution on behalf of its copyright owner.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.28%. Comparing base (2291e46) to head (7268ca1).

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #264   +/-   ##
=========================================
  Coverage     81.28%   81.28%           
  Complexity      316      316           
=========================================
  Files            35       35           
  Lines           967      967           
  Branches         88       88           
=========================================
  Hits            786      786           
  Misses          129      129           
  Partials         52       52           

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