[Refactor] Fix linter error in dumper.go & path.go

[fredzqm]

This PR has no behavior change. Hence, no tests change.

It makes the behavior of isZero for boolean field explicit and address the linter warnings in a good way.

Previously, we got this linter error in master commit's CI result

$ golangci-lint run  ast/dumper.go --fix
ast/dumper.go:153:9: reflectvaluecompare: avoid using reflect.DeepEqual with reflect.Value (govet)
        return reflect.DeepEqual(v.Interface(), reflect.Zero(v.Type()))
               ^
1 issues:
* govet: 1

Fixed another linter error that pops up after the prev issue is fixed:

run golangci-lint
  Running [/home/runner/golangci-lint-2.10.1-linux-amd64/golangci-lint config path] in [/home/runner/work/gqlparser/gqlparser] ...
  Running [/home/runner/golangci-lint-2.10.1-linux-amd64/golangci-lint config verify] in [/home/runner/work/gqlparser/gqlparser] ...
  Running [/home/runner/golangci-lint-2.10.1-linux-amd64/golangci-lint run  --timeout 5m] in [/home/runner/work/gqlparser/gqlparser] ...
  Error: ast/path.go:30:4: QF1012: Use fmt.Fprintf(...) instead of WriteString(fmt.Sprintf(...)) (staticcheck)
  			str.WriteString(fmt.Sprintf("[%d]", v))
  			^
  1 issues:
  * staticcheck: 1
  
  Error: issues found
  Ran golangci-lint in 20872ms

I have:

• Added tests covering the bug / feature
• Updated any relevant documentation

[coveralls]

coverage: 87.157% (-0.02%) from 87.18%
when pulling 9caeee1 on fredzqm:master
into 48a3d5e on vektah:master.

[StevenACoffman]

Thanks so much! I really appreciate it!