Convert from glide to go modules

[LCartwright]

go get -u github.com/nshmura/dsio fails with the following error:

❯ go get -u github.com/nshmura/dsio
# github.com/nshmura/dsio/core
.gvm/pkgsets/go1.15/global/src/github.com/nshmura/dsio/core/context.go:23:19: c.GlobalBool undefined (type *cli.Context has no field or method GlobalBool)
.gvm/pkgsets/go1.15/global/src/github.com/nshmura/dsio/core/log.go:41:41: undefined: cli.ExitError

go env

❯ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/laurence/.cache/go-build"
GOENV="/home/laurence/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/laurence/.gvm/pkgsets/go1.15/global/pkg/mod"
GONOPROXY="github.com/paymentsense/*"
GONOSUMDB="github.com/paymentsense/*"
GOOS="linux"
GOPATH="/home/laurence/.gvm/pkgsets/go1.15/global"
GOPRIVATE="github.com/paymentsense/*"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/laurence/.gvm/gos/go1.15"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/laurence/.gvm/gos/go1.15/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build518681876=/tmp/go-build -gno-record-gcc-switches"

In order to fix this, all I've needed to do is convert the project to go modules