[sql] Fix typo in error message.

sql/connection.cc

Index: sql/connection.cc
diff --git a/sql/connection.cc b/sql/connection.cc
index 3d584a65e11095a8e0c86becdcf16486fa3c306b..44cb5979884f5a4e8cd0b2a72f95651ca37d43e1 100644
--- a/sql/connection.cc
+++ b/sql/connection.cc
@@ -1145,7 +1145,7 @@ void Connection::RollbackTransaction() {
 
 bool Connection::CommitTransaction() {
   if (!transaction_nesting_) {
-    DLOG_IF(FATAL, !poisoned_) << "Committing back a nonexistent transaction";
+    DLOG_IF(FATAL, !poisoned_) << "Committing a nonexistent transaction";
     return false;
   }
   transaction_nesting_--;