Docu update.

README

@@ -67,7 +67,7 @@ Building and installing it:
 Porting:
 
      This package was designed for maximum portability. It is written entirely
-     in ISO C++14 and ANSI C99, and will compile on most UNIX platforms.
+     in ISO C++17 and ANSI C99, and will compile on most UNIX platforms.
      
 Contact:
 

doc/tex/install.tex

@@ -2,7 +2,7 @@
 
 This section describes how to build {\CDO} from the sources on a UNIX system.
 {\CDO} uses the GNU configure and build system for compilation.
-The only requirement is a working ISO C++14 and ANSI C99 compiler.
+The only requirement is a working ISO C++17 and ANSI C99 compiler.
 
 %First go to the \href{https://www.mpimet.mpg.de/cdo/download.html}{\texttt{download}} page
 %(\texttt{https://www.mpimet.mpg.de/\\,cdo/download.html}) to get the latest distribution,