Fix memory leak in ExpandedSQL (#738)

Fixes: #733

sqlite3_trace.go

diff --git a/sqlite3_trace.go b/sqlite3_trace.go
index ee93a0f..51cb22e 100644
--- a/sqlite3_trace.go
+++ b/sqlite3_trace.go
@@ -89,6 +89,7 @@
 	}
 
 	expSQLiteCStr := C.sqlite3_expanded_sql((*C.sqlite3_stmt)(pStmt))
+	defer C.sqlite3_free(unsafe.Pointer(expSQLiteCStr))
 	if expSQLiteCStr == nil {
 		fillDBError(&info.DBError, db)
 		return