go mod dependency mgmt and workound bug fix to broken dependency

See my comment in https://github.com/immutability-io/vault-ethereum/issues/51

Description

introduce two go mod init generated files: go.mod and go.sum using latest available dependencies except for github.com/miguelmota/go-coinmarketcap which has a bad commit at this time (so using the . prior commit)

Motivation and Context

When a breaking api change happens to any package in the transitive dependencie then this project would also break. This dependency management helps stabilize the builds but special conscious care must be made to pull in new version dependencies or new packages altogether. Read about go module here: https://github.com/golang/go/wiki/Modules

https://github.com/immutability-io/vault-ethereum/issues/51

How Has This Been Tested?

The build has beeen tested. The runtime needs to be tested still.

go install (after using go mod and go dep to set the base dependency versions

go version go1.11.4 darwin/amd64

Screenshots (if appropriate):

Types of changes

[x ] Documentation enhancement
[x ] Bug fix (non-breaking change which fixes an issue)
[ x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[ ] My code follows the code style of this project.
[x] My change requires a change to the documentation.
[ x] I have updated the documentation accordingly.
[x ] I have read the CONTRIBUTING document.

immutability-io / vault-ethereum