fix: work with new simple-git output

Author: David Bushong

lib/commands/merge-back.js

@@ -84,7 +84,8 @@ async function tryMerge(deps, from, to, main) {
   try {
     // https://github.com/steveukx/git-js/issues/204
     const output = await git.merge([from]);
-    if (/\nCONFLICT /.test(output)) throw new Error(output);
+    if (output.failed)
+      throw new Error(output.conflicts.map(c => `${c}`).join('\n\n'));
   } catch (err) {
     log('Automated merge failed; creating feature branch for resolution');
     await createFeatureMerge(deps, from, main); // will throw