spec: use "or" instead of "/" in License line
rpmlint on Fedora 31 complains about "LGPLv2+ / MIT" because "/" is not
allowed.  Use "or" instead.
Fixes:
("Include MIT notice in rpm spec and debian package file")
@@ -2,7 +2,7 @@ Name: liburing
Version: 0.6
Release: 1%{?dist}
Summary: Linux-native io_uring I/O access library
-License: LGPLv2+ / MIT
+License: LGPLv2+ or MIT
Source0: https://brick.kernel.dk/snaps/%{name}-%{version}.tar.gz
Source1: https://brick.kernel.dk/snaps/%{name}-%{version}.tar.gz.asc
URL: https://git.kernel.dk/cgit/liburing/
