bump minimal version in documentation (#787) (#788)

Author: Anaethelion

.doc/getting-started.asciidoc

@@ -9,7 +9,7 @@ fully typed API. This getting started shows you examples of both APIs.
 [discrete]
 === Requirements
 
-Go version 1.13+
+Go version 1.20+
 
 [discrete]
 === Installation 

CONTRIBUTING.md

@@ -13,7 +13,7 @@ before we can accept pull requests from you.
 
 ### Prerequisites
 
-You need at least Go 1.13 to build the project.
+You need at least Go 1.20 to build the project.
 
 Docker is used for some tests to spawn an Elasticsearch server.