feat(modules): Add go.mod for Go modules

[robinjoseph08]

What

• use go v1.13.3
• switch from dep to go modules
• switch from gometalinter to golangc-lint
• ignore bin directory since thats where all tools are now being installed into
• build against multiple versions of go
• add version badge to readme
• change module path to github.com/robinjoseph08/go-pg-migrations/v2 to allow those who are not using go modules yet to keep using v1
• pin to version v9 of go-pg, update all paths to use v9, and update some code for v9
• update example dockerfile in readme to use go modules
• add a tools.go