fmt: uses 6.0 as th minimal version

fmt from the system on Fedora is not working properly

Change-Id: Ic28a976e110fc168faa3b985cc0852a31ec34114

contrib/src/fmt/rules.mak

@@ -3,7 +3,7 @@ FMT_VERSION := 6.1.2
 FMT_URL := https://github.com/fmtlib/fmt/archive/$(FMT_VERSION).tar.gz
 
 PKGS += fmt
-ifeq ($(call need_pkg,'fmt >= 5.3'),)
+ifeq ($(call need_pkg,'fmt >= 6.0'),)
 PKGS_FOUND += fmt
 endif