Fixed errcheck with abspath

[hori-ryota]

Errcheck output errors using relative path format but when failed to check packages using absolute path.

Now, absolute path inputed, vim-go errcheck add unnecessary prefix like

/your/gopath/your/gopath/filepath.go

Errcheck introduced abspath options so fixed by using it.

[fatih]

Hi @hori-ryota Thanks for the PR! Can you please add a test case so I can test it ? I would appreciate it.

[hori-ryota]

Where are tests implemented?

Errcheck will failed unbuildable package such as syntax error.

[fatih]

@hori-ryota I meant a demo test file you can add so I can test what has changed ?

[fatih]

@hori-ryota ping. I've asked for a demo.go file which fails, but is fixed with this PR. It's all so I can test it and reproduce your fix :) Let me know if I can do something here.

[hori-ryota]

oh, solly for the delay.

Please test with following demo.go

package main

func main() {
    demo := "demo"
}

[fatih]

Thanks @hori-ryota. We fixed the issue with errcheck multiple times. I'm going to eventually remove it in the future because we have now :GoMetaLinter and maintaining it is simpler.