Update Dockerfile

[SparkLee]

Good job, it can fix the problem I encountered when running the command "docker build -t xxx":

=> [builder 2/4] COPY . /src                                                                                                                                              0.1s
=> [builder 3/4] WORKDIR /src                                                                                                                                             0.0s
=> ERROR [builder 4/4] RUN GOPROXY=https://goproxy.cn make build                                                                                                         14.9s
------                                                                                                                                                                          
> [builder 4/4] RUN GOPROXY=https://goproxy.cn make build:                                                                                                                     
#0 0.515 go get github.com/go-kratos/kratos/v2@v2.6.2                                                                                                                           
#0 9.475 note: module requires Go 1.18

[songzhibin97]

130