Modified vendor code in `gcfg`

Hello!

While trying to consume `gh-ost` as a go library, I included it in an application that is using `godep` to manage the dependencies. When `gh-ost` is pulled in, it ignores the project's `vendor` directory and installs the dependencies needed by `gh-ost` into the top level vendor directory in the consuming application. A while back there were some modifications to the `gcfg` library checked in to this repo to add the `RelaxedParserMode` (https://github.com/github/gh-ost/commit/4774b67ffdc6e87837ca1a2d413fe416f938eeba#diff-a44ddd65a1cbf0f5ef8b69bde1953565). When `godep` resolves `gcfg` the upstream version, I get the following compiler error because this flag is not present:
```
us-nmathew1:migrant nikhil.mathew$ go run ./src/main.go
# github.com/gusto/migrant/vendor/github.com/github/gh-ost/go/base
vendor/github.com/github/gh-ost/go/base/context.go:689: undefined: gcfg.RelaxedParserMode
vendor/github.com/github/gh-ost/go/base/context.go:690: undefined: scanner.RelaxedScannerMode
```

Any ideas on how best to proceed here? Is it possible to remove this flag and use the upstream `gcfg`? Currently, I've had to make these same changes in my consuming application's vendor directory and be careful when updating `godep` to maintain the changes. Relatedly, any thoughts on using a tool like `godep` to manage the dependencies?