distro/rpm: properly escape %BASE_VERSION

rpm %() macro requires double escaping

distro/rpm/knot.spec

@@ -3,7 +3,7 @@
 
 %define GPG_CHECK 0
 %define VERSION __VERSION__
-%define BASE_VERSION %(echo %{version} | sed 's/^\([^.]\+\.[^.]\+\).*/\1/')
+%define BASE_VERSION %(echo "%{version}" | sed 's/^\\([^.]\\+\\.[^.]\\+\\).*/\\1/')
 %define repodir %{_builddir}/%{name}-%{version}
 
 Summary:	High-performance authoritative DNS server