chore(version-info): better error msg if not tags

Author: petebacondarwin

lib/versions/version-info.js

@@ -136,6 +136,12 @@ var getSnapshotVersion = function() {
     })
     .last();
 
+  if ( !version ) {
+    throw new Error("No valid versions can be found that match the current branch (" +
+      currentPackage.branchVersion + ").\n" +
+      "Try running `git fetch -t` to download the tags from the repository.");
+  }
+
   // We need to clone to ensure that we are not modifying another version
   version = semver(version.raw);