fix(backup): Don't show warnng on current major

refs: TryGhost/Toolbox#334
refs: #468

- Only show the warning about upgrading if there's a major upgrade to do

lib/commands/backup.js

@@ -23,11 +23,13 @@ class BackupCommand extends Command {
         }
 
         // Get the latest version in our current major
-        const {latestMajor} = await loadVersions();
+        const {latestMajor, latest} = await loadVersions();
         const activeMajor = semver.major(instance.version);
         const latestMinor = latestMajor[`v${activeMajor}`];
 
-        if (instance.version !== latestMinor && !argv.force) {
+        const isBehindByMajor = semver.diff(instance.version, latest) === 'major';
+
+        if (instance.version !== latestMinor && isBehindByMajor && !argv.force) {
             const currentMajor = semver.major(instance.version);
 
             throw new CliError({