Update version for release (#2269)

Author: Ron

versions/3.1.0.md

@@ -1,6 +1,6 @@
 # OpenAPI Specification
 
-#### Version 3.1.0
+#### Version 3.1.0-rc0
 
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [BCP 14](https://tools.ietf.org/html/bcp14) [RFC2119](https://tools.ietf.org/html/rfc2119) [RFC8174](https://tools.ietf.org/html/rfc8174) when, and only when, they appear in all capitals, as shown here.
 
@@ -3419,7 +3419,7 @@ Two examples of this:
 
 Version   | Date       | Notes
 ---       | ---        | ---
-3.1.0     | TBD        | TBD
+3.1.0-rc0 | 2020-06-18 | rc0 of the 3.1 specification
 3.0.3     | 2020-02-20 | Patch release of the OpenAPI Specification 3.0.3
 3.0.2     | 2018-10-08 | Patch release of the OpenAPI Specification 3.0.2
 3.0.1     | 2017-12-06 | Patch release of the OpenAPI Specification 3.0.1