Replace yajl-ruby with the json gem for JSON handling (#174)

Since the yajl-ruby gem depends on a deprecated Ruby C API, it cannot be
installed with Ruby 4.1.

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

lib/fluent/plugin/out_sql.rb

@@ -99,7 +99,7 @@ def import(chunk, output)
             columns |= new_record.keys
             records << @model.new(new_record)
           rescue => e
-            args = {error: e, table: @table, record: Yajl.dump(data)}
+            args = {error: e, table: @table, record: JSON.generate(data)}
             @log.warn "Failed to create the model. Ignore a record:", args
           end
         }