Fix revisions (modelica#3423)

* Avoid link to modelica.org/documents

* Plural

* Update chapters/revisions.tex

Co-authored-by: Malte Lenz <malte.lenz@gmail.com>

chapters/revisions.tex

@@ -2,8 +2,7 @@ \chapter{Modelica Revision History}\label{modelica-revision-history}
 
 This appendix described the history of the Modelica Language Design, and its contributors.
 This appendix is just present for historical reasons and is not normative.
-The current version of this document is available from \url{https://modelica.org/documents}.
-All versions of this document, and the list of changes is available at \url{https://specification.modelica.org}.
+The current version, as well as all previous versions of this document, and the list of changes are available at \url{https://specification.modelica.org}.
 
 The members of the Modelica Association project \emph{Modelica Language} (MAP-Lang) contributed to the Modelica specification.