Fix test suite

[jmini]

I have tried to run `` against the examples I found in Swagger folder.

cd openapi-diff/src/modeler/AutoRest.Swagger.Tests/Resource/Swagger
oad compare old/added_path.json new/added_path.json
oad compare old/added_property_in_response.json new/added_property_in_response.json
oad compare old/added_required_property.json new/added_required_property.json
oad compare old/changed_operation_id.json new/changed_operation_id.json
oad compare old/enum_values_changed.json new/enum_values_changed.json
oad compare old/misc_checks_01.json new/misc_checks_01.json
oad compare old/misc_checks_02.json new/misc_checks_02.json
oad compare old/operation_check_01.json new/operation_check_01.json
oad compare old/operation_check_02.json new/operation_check_02.json
oad compare old/operation_check_03.json new/operation_check_03.json
oad compare old/operation_check_04.json new/operation_check_04.json
oad compare old/operation_check_05.json new/operation_check_05.json
oad compare old/param_check_01.json new/param_check_01.json
oad compare old/readonly_changes.json new/readonly_changes.json
oad compare old/recursive_model.json new/recursive_model.json
oad compare old/removed_definition.json new/removed_definition.json
oad compare old/removed_operation.json new/removed_operation.json
oad compare old/removed_path.json new/removed_path.json
oad compare old/removed_property.json new/removed_property.json
oad compare old/required_parameter.json new/required_parameter.json
oad compare old/response_check_01.json new/response_check_01.json
oad compare old/type_changed.json new/type_changed.json
oad compare old/version_check_01.json new/version_check_01.json
oad compare old/version_check_02.json new/version_check_02.json
oad compare old/version_check_03.json new/version_check_03.json
oad compare old/version_check_04.json new/version_check_04.json

I got a lot of errors, preventing me to get the results.
Example:

$ oad compare old/added_path.json new/added_path.json
FATAL: swagger-document/loader - FAILED
FATAL: Error: File 'file:///___/openapi-diff/src/modeler/AutoRest.Swagger.Tests/Resource/Swagger/new/added_path.json' is not a valid OpenAPI 2.0 definition (expected 'swagger: 2.0')
  Error: File 'file:///___/openapi-diff/src/modeler/AutoRest.Swagger.Tests/Resource/Swagger/new/added_path.json' is not a valid OpenAPI 2.0 definition (expected 'swagger: 2.0')

With this Pull Request, I have updated all Swagger definitions in order to be able to run the tool.

• definition declaration: "swagger": 2.0 => "swagger": "2.0"
• tag => tags
• set paths everywhere
• set responses everywhere
• add description in responses when missing
• remove "type": "object" when a schema is defined
• remove collectionFormat

[msftclas]

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