http接口获取到的 mbvar转prometheus metrics 格式, 提示格式非法

[highkic]

Describe the bug (描述bug)
通过brpc_metrics接口获取mbvar 转化来的多lables guage打点，提示type非法
具体的值:

# HELP lat_rank_score_total_latency{system="unknown",module="unknown",server="rank_server_nbase",status="0"}
# TYPE lat_rank_score_total_latency{system="unknown",module="unknown",server="rank_server_nbase",status="0"} gauge
lat_rank_score_total_latency{system="unknown",module="unknown",server="rank_server_nbase",status="0"} 22

To Reproduce (复现方法)

typedef bvar::MultiDimension<bvar::LatencyRecorder> MLatencyRecorder;
MLatencyRecorder lat_rank_score_total("lat_rank_score_total", {"system", "module", "server", "status"});
mbvar_dump=true
mbvar_dump_format= prometheus

打点收集，然后prometheus收集组件通过 http://$ip:$port/brpc_metrics获取打点结果，提示错误

invalid metirc type "system=\"square\" ****** gauge"

Expected behavior (期望行为)
能正常收集

Versions (各种版本)
OS: linux
Compiler: gcc 7.3.1
brpc: 1月10号版master
protobuf: 3.6.0

Additional context/screenshots (更多上下文/截图)

[wwbmmm]

@serverglen 有空看下

[highkic]

请问这个问题修复分支合入master了么