Use SPDX format for license field

See [the wiki][1] for details.

[1]: https://fedoraproject.org/wiki/Changes/SPDX_Licenses_Phase_1

will-crash.spec

@@ -14,7 +14,7 @@ Release:        2%{?dist}
 Summary:        Set of crashing executables written in various languages
 
 Group:          Development/Tools
-License:        GPLv3
+License:        GPL-3.0-only
 URL:            https://github.com/abrt/will-crash
 Source0:        https://github.com/abrt/%{name}/releases/download/v%{version}/%{name}-%{version}.tar.gz