build: migrate to C++17

Change-Id: Ic66b1703fc7d1d51d61c442de859e0921c0bdd7a
diff --git a/README.md b/README.md
index 6523357..8d03a64 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 [![CI](https://github.com/named-data/PSync/actions/workflows/ci.yml/badge.svg)](https://github.com/named-data/PSync/actions/workflows/ci.yml)
 [![Docs](https://github.com/named-data/PSync/actions/workflows/docs.yml/badge.svg)](https://github.com/named-data/PSync/actions/workflows/docs.yml)
-![Language](https://img.shields.io/badge/C%2B%2B-14-blue)
+![Language](https://img.shields.io/badge/C%2B%2B-17-blue)
 ![Latest version](https://img.shields.io/github/v/tag/named-data/PSync?label=Latest%20version)
 
 The PSync library implements the