Crank to C++17 to match libphonenumber and abseil-cpp.

Index: src/addressbook/libebook-contacts/CMakeLists.txt
--- src/addressbook/libebook-contacts/CMakeLists.txt.orig
+++ src/addressbook/libebook-contacts/CMakeLists.txt
@@ -82,7 +82,7 @@ if(ENABLE_PHONENUMBER)
 	)
 
 	target_compile_features(ephonenumber-private PUBLIC
-		cxx_std_14
+		cxx_std_17
 	)
 
 	target_compile_options(ephonenumber-private PUBLIC
