Support dependencies with package names that include ";"

[li-peng-dd]

I noticed that if you try to start a service with a proto file that includes a dependency on something with package like go_package=github.com/golang/protobuf/protoc-gen-go/descriptor;descriptor, it fails with:

2019/09/05 03:16:17 Failed to generate server formatting 20:19: invalid import path: "github.com/golang/protobuf/protoc-gen-go/descriptor;descriptor" (and 1 more errors)

This is because server.tmpl just naively uses the package declaration as the import statement, which results in invalid like above. It can be fixed by truncating the package declaration at the semicolon.

[li-peng-dd]

@jekiapp I propose #26 as fix for this.

[jekiapp]

solved in #27 with example. api.proto has declaration of go_package with ;