Jenkinsfile: Try to fix env var usage.

Jenkinsfile

@@ -9,8 +9,8 @@ node {
          stage "test"
          sh 'env'
          sh "curl https://glide.sh/get | sh"
-         sh "mv $GOPATH/src/github.com/UNINETT $GOPATH/src/github.com/uninett"
-         sh "cd $GOPATH/src/github.com/uninett/jwt-tokenissuer"
+         sh "mv ${GOPATH}/src/github.com/UNINETT ${GOPATH}/src/github.com/uninett"
+         sh "cd ${GOPATH}/src/github.com/uninett/jwt-tokenissuer"
          sh "glide install"
          sh "make test"
 
@@ -22,7 +22,7 @@ node {
          stage "package"
          unstash 'binary'
          sh "mv jwt-tokenissuer /src/"
-         sh "fpm -s dir /src=/opt/jwt-tokenissuer -t deb -n jwt-tokenissuer -v ${env.VERSION_STRING}"
+         sh "fpm -s dir /src=/opt/jwt-tokenissuer -t deb -n jwt-tokenissuer -v ${VERSION_STRING}"
          archive includes: '*.deb'
      }
 }