.api file does not support prefix only with "-"

[litecy]

Describe the bug .api file does not support prefix only with "-"

Some of my url prefix is "/-/", it is VALID for http

but i can't use in api file.

To Reproduce Steps to reproduce the behavior, if applicable:

1. The code is

@server ( group: main prefix: /-/ ) service trafficredirect { @doc ( summary: "ping" ) @handler PingHandler get /ping (PingReq) returns (PingResp) }

@server ( group: main prefix: /- ) service trafficredirect { @doc ( summary: "ping" ) @handler PingHandler get /ping (PingReq) returns (PingResp) }

2. The error is

syntax error: expected 'IDENT', got '-'

**Expected behavior**

support valid char or char combination in the prefix

**Screenshots**
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**Environments (please complete the following information):**
- OS: darwin
- goctl version 1.8.4 darwin/amd64

**More description**
Add any other context about the problem here.