fix: chdir to dir of spec file to fix parsing error of refs

[authurlan]

• Found error:

$ pwd
/home/foo/jsonrpc
$ jrgen docs-html sub/index.json
/home/foo/jsonrpc/node_modules/jrgen/src/utils.js:201                       
        throw error;             
        ^                                     
                                                                                                   
ResolverError: Error opening file "/home/foo/jsonrpc/methods/session/login.json" 
ENOENT: no such file or directory, open '/home/foo/jsonrpc/methods/session/login.json'          
    at ReadFileContext.callback (/home/foo/jsonrpc/node_modules/@apidevtools/json-schema-ref-parser/lib/resolvers/file.js:52:20)
    at FSReqCallback.readFileAfterOpen [as oncomplete] (fs.js:282:13) {
  code: 'ERESOLVER',                                                                               
  source: '/home/foo/jsonrpc/methods/session/login.json',                   
  path: null,                                
  toJSON: [Function: toJSON],                                                                      
  ioErrorCode: 'ENOENT',                                                                           
  [Symbol(nodejs.util.inspect.custom)]: [Function: inspect]                                        
}                                                                                                  
error Command failed with exit code 1.

• Project files:

jsonrpc
|- sub
|  |- methods
|  |  |- session
|  |     |- login.json
|  |- index.json
|- node_modules
|- package.json

index.json uses "./methods/session/login.json" to refer login.json

[mzernetsch]

I think because of 17334593fc54c5db462b679dd4b46a649c677dbe it should work correctly now. Could you please test if the problem is still present after the next release?