Check is the codes is formated in travis ci

[aisk]

I saw current codes have not been formatted yet, so just added a travis ci step to check it, and I think this should work since this PR is failed now: https://travis-ci.org/github/goby-lang/goby/builds/738725791

I'll add another commit to format the codes and let CI pass again.

[aisk]

For go's format rules, I think if we continues using "Merge pull request" button to merge PRs, it will make the master's codes been un-formatted again. I think we should using "Rebase" method to submit PRs, and rebase every PR before submit to avoid this.

[aisk]

I saw goby is using go module and the old vendor folder still here, and having code not been formatted, so just removed this folder, I don't know whether this is suitable?

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@1dd1905). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #864   +/-   ##
=========================================
  Coverage          ?   80.92%           
=========================================
  Files             ?       54           
  Lines             ?     6775           
  Branches          ?        0           
=========================================
  Hits              ?     5483           
  Misses            ?     1067           
  Partials          ?      225           

Impacted Files	Coverage Δ
vm/class.go	86.72% <0.00%> (ø)
vm/validate.go	48.92% <0.00%> (ø)
native/ripper/ripper.go	70.37% <0.00%> (ø)
vm/range.go	94.11% <0.00%> (ø)
vm/float.go	76.64% <0.00%> (ø)
vm/http_client.go	57.89% <0.00%> (ø)
vm/concurrent_hash.go	96.22% <0.00%> (ø)
vm/repl.go	80.00% <0.00%> (ø)
compiler/parser/parser.go	93.96% <0.00%> (ø)
vm/block.go	63.33% <0.00%> (ø)
... and 44 more

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[st0012]

I understand the intention behind this change, but I don't feel the need to format all the code, especially not the vendor files. We use vendor because unlike normal applications, Goby's dependencies should be as steady as possible. And I want to minimize the risk that if a dependency is removed from the source, we won't be able to build our source code again.