Adjust gnome-shell requirement

With the new version scheme, extensions must only match the major
gnome-shell version. While not enforced by the shell, it still makes
sense to match minor versions for development releases, but as the
package version uses "~" instead of "." in that case, matching on
the first field when splitting by dot gives us the desired behavior
for both stable and unstable versions:

 43~rc   → 43~rc
 43~rc.1 → 43~rc
 43.0    → 43
 43.1    → 43

gnome-shell-extensions.spec

@@ -1,6 +1,6 @@
 %global major_version %%(cut -d "." -f 1 <<<%{version})
 # Minimum GNOME Shell version supported
-%global min_gs_version %%(cut -d "." -f 1-3 <<<%{version})
+%global min_gs_version %%(cut -d "." -f 1 <<<%{version})
 
 %global pkg_prefix gnome-shell-extension
 %global tarball_version %%(echo %{version} | tr '~' '.')