Remove Array markers around op.requestBody def.

As discussed [here](google/gnostic#35 (comment))

Author: MikeRalphson

versions/3.0.md

@@ -763,7 +763,7 @@ Field Name | Type | Description
 <a name="operationExternalDocs"></a>externalDocs | [External Documentation Object](#externalDocumentationObject) | Additional external documentation for this operation.
 <a name="operationId"></a>operationId | `string` | Unique string used to identify the operation. The id MUST be unique among all operations described in the API. Tools and libraries MAY use the operationId to uniquely identify an operation, therefore, it is recommended to follow common programming naming conventions.
 <a name="operationParameters"></a>parameters | [[Parameter Object](#parameterObject) \| [Reference Object](#referenceObject)] | A list of parameters that are applicable for this operation. If a parameter is already defined at the [Path Item](#pathItemParameters), the new definition will override it but can never remove it. The list MUST NOT include duplicated parameters. A unique parameter is defined by a combination of a [name](#parameterName) and [___location](#parameterIn). The list can use the [Reference Object](#referenceObject) to link to parameters that are defined at the [OpenAPI Object's parameters](#oasParameters).
-<a name="operationRequestBody"></a>requestBody | [[Request Body Object](#requestBodyObject) \| [Reference Object](#referenceObject)] | The request body applicable for this operation.  The `requestBody` is only supported in HTTP methods where the [HTTP 1.1 specification](https://tools.ietf.org/html/rfc7231#section-4.3.1) has explicitly defined semantics for request bodies.  In other cases where the HTTP spec is vague, `requestBody` SHALL be ignored by consumers.
+<a name="operationRequestBody"></a>requestBody | [Request Body Object](#requestBodyObject) \| [Reference Object](#referenceObject) | The request body applicable for this operation.  The `requestBody` is only supported in HTTP methods where the [HTTP 1.1 specification](https://tools.ietf.org/html/rfc7231#section-4.3.1) has explicitly defined semantics for request bodies.  In other cases where the HTTP spec is vague, `requestBody` SHALL be ignored by consumers.
 <a name="operationResponses"></a>responses | [Responses Object](#responsesObject) | **Required.** The list of possible responses as they are returned from executing this operation.
 <a name="operationCallbacks"></a>callbacks | [Callbacks Object](#callbacksObject) | The list of possible callbacks as they are returned from executing this operation.
 <a name="operationDeprecated"></a>deprecated | `boolean` | Declares this operation to be deprecated. Consumers SHOULD refrain from usage of the declared operation. Default value is `false`.