fix: verify the local branch is up to date with the remote one

lib/git.js

@@ -131,6 +131,17 @@ async function verifyTagName(tagName) {
   }
 }
 
+/**
+ * Verify the local branch is up to date with the remote one.
+ *
+ * @param {String} branch The repository branch for which to verify status.
+ *
+ * @return {Boolean} `true` is the HEAD of the current local branch is the same as the HEAD of the remote branch, `false` otherwise.
+ */
+async function isBranchUpToDate(branch) {
+  return isRefInHistory(await execa.stdout('git', ['rev-parse', `${branch}@{u}`]));
+}
+
 module.exports = {
   gitTagHead,
   gitTags,
@@ -143,4 +154,5 @@ module.exports = {
   tag,
   push,
   verifyTagName,
+  isBranchUpToDate,
 };