Update golang-jwt/jwt/v4 version

[BamButz]

PR regarding #898

The subject of #898 seems to be already accomplished.
In this PR, I've upgraded github.com/golang-jwt/jwt/v4 to version 4.1.0 to be fully up-to-date on this.

closes #898

[seokho-son]

Hello @BamButz ~! Thank you for the contribution. Welcome to CB-Tumblebug project :)

You are right. The guide in the issue #898 is not appropriate :)
CB-Tumblebug go.mod already uses github.com/golang-jwt/jwt/v4

The problem (github.com/dgrijalva/jwt-go) comes from go.sum file not from the go.mod.

Other external packages that CB-Tumblebug utilize include github.com/dgrijalva/jwt-go as follows.

---

son@son:~/go/src/github.com/cloud-barista/cb-tumblebug$ go mod graph | grep github.com/dgrijalva/jwt-go

github.com/labstack/echo/v4@v4.2.1 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/dgrijalva/jwt-go/v4@v4.0.0-preview1 golang.org/x/xerrors@v0.0.0-20191204190536-9bdfabe68543
github.com/labstack/echo/v4@v4.0.0 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/Azure/go-autorest/autorest/adal@v0.8.3 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/go-kit/kit@v0.10.0 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/influxdata/influxdb@v1.8.0 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/labstack/echo/v4@v4.1.11 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/Azure/go-autorest/autorest/adal@v0.8.2 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/Azure/go-autorest/autorest/adal@v0.8.1 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
go.etcd.io/etcd@v0.0.0-20191023171146-3cf2f69b5738 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/Azure/go-autorest/autorest/adal@v0.5.0 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/influxdata/influxdb@v1.9.2 github.com/dgrijalva/jwt-go/v4@v4.0.0-preview1
github.com/Azure/go-autorest/autorest/adal@v0.8.0 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/labstack/echo/v4@v4.3.0 github.com/dgrijalva/jwt-go@v3.2.0+incompatible
github.com/cloud-barista/cb-spider@v0.4.5 github.com/dgrijalva/jwt-go@v3.2.0+incompatible

We need to use updated version for those packages to fully resolve #898

Anyway! This PR is acceptable and meaningful (fully up-to-date version).
So, LGTM !

[seokho-son]

/lgtm

[seokho-son]

@all-contributors please add @BamButz for code

[allcontributors]

@seokho-son

I've put up a pull request to add @BamButz! 🎉

[seokho-son]

@BamButz I added you in contributor list of CB-Tumblebug project :)
https://github.com/cloud-barista/cb-tumblebug#contributors-

[seokho-son]

Also, please fill free to open a issue regarding the package security issue.