fix(frontends/lean/interactive): go-to-definition for relative imports
fix(frontends/lean/interactive): go-to-definition for relative imports

Fixes leanprover/vscode-lean#58.

leanprover/lean,dselsam/lean,avigad/lean,johoelzl/lean,leodemoura/lean,leanprover/lean,fpvandoorn/lean,leanprover-community/lean,digama0/lean,johoelzl/lean,Kha/lean,digama0/lean,Kha/lean,leanprover/lean,dselsam/lean,avigad/lean,leanprover-community/lean,johoelzl/lean,leanprover-community/lean,dselsam/lean,johoelzl/lean,leodemoura/lean,dselsam/lean,avigad/lean,leanprover/lean,Kha/lean,avigad/lean,leodemoura/lean,fpvandoorn/lean,leodemoura/lean,digama0/lean,leanprover/lean,leodemoura/lean,avigad/lean,Kha/lean,johoelzl/lean,Kha/lean,dselsam/lean,fpvandoorn/lean,leanprover-community/lean,fpvandoorn/lean,leodemoura/lean,digama0/lean,fpvandoorn/lean,dselsam/lean,leanprover/lean,leanprover-community/lean,avigad/lean,leanprover-community/lean,digama0/lean,fpvandoorn/lean,johoelzl/lean,digama0/lean,Kha/lean